CHEMTUTOR 9

An atom has a zero oxidation number when it is in its (elemental, ionic) state.

elemental

Assign oxidation numbers to all elements in NH3 What is the oxidation number of hydrogen? (rule 6)

+1

RULE 6: The usual oxidation number for hydrogen is +1. For example: The hydrogen in HCl has an oxidation number = +1. What is the oxidation number of hydrogen in H2O?

+1

What is the oxidation number of Cl in ClF?

+1

RULE 3: The oxidation numbers of groups IA and IIA elements when combined in a compound are always +1 and +2 respectively. For example, The oxidation number of Ca in CaCl2 is +2 because Ca is in group IIA. The oxidation number of Na in Na2O is +1 because Na is in group IA. Elements in group IA have an oxidation number = _____. Elements in group IIA have an oxidation number = _____.

+1, +2

Assign oxidation numbers to all elements in H3PO4. H ox # ___ P ox # ___ O ox # ___

+1, +5, -2

Assign oxidation numbers to all elements in KMnO4: Potassium ox # ___ Manganese ox # ___ Oxygen ox # ___

+1, +7, -2

RULE 2: The oxidation number of any monatomic ion is equal to the charge on the ion. For example, Na+, a monatomic ion, has an oxidation number of +1. The ion S2- has an oxidation number of -2. What is the oxidation number of Ca2+?

+2

What is the oxidation number of Mg in Mg3N2?

+2

Assign oxidation numbers to all elements in NO. Nitrogen ox # ___ Oxygen ox # ___

+2, -2

Consider the reaction: STEP 1: Determine oxidation numbers for all elements involved in the reaction. CO C ox # ____ O ox # ____ O2 O ox # ____ CO2 C ox # ____ O ox # ____

+2, -2, 0, +4, -2

STEP 1: Determine oxidation numbers for all elements involved in the reaction. FeO = Fe ox # _+2_ O ox # _-2_ C = C ox # _0_ Fe = Fe ox # _0_ CO = C ox # _+2_ O ox # _-2_

+2, -2, 0, 0, +2, -2

Assign oxidation numbers to all elements in TiCl4. Ti ox # ___ Cl ox # ___

+4, -1

Assign oxidation numbers to all elements in TiO2. Ti ox # ___ O ox # ___

+4, -2

Consider the reaction: STEP 1: Determine oxidation numbers for all elements involved in the reaction. Elemental S ox # = 0 Elemental O (from O2) ox # = 0 What is the oxidation number of S in SO2? What is the oxidation number of O in SO2?

+4, -2

Many elements have a range of oxidation numbers. Depending on which compound they are in, the oxidation number will be different. For example, nitrogen (Group VA) has oxidation numbers from -3 to +5. NH3 N2O NO N2O3 NO2 N2O5 -3 +1 +2 +3 +4 +5 What is nitrogen's highest oxidation number?

+5

What is the oxidation number of Cl in ClO3- ?

+5

Assign oxidation numbers to all elements in N2O5. Nitrogen ox # ___ Oxygen ox # ___

+5, -2

What is the oxidation number of Cl in Cl2O7?

+7

RULE 5: The usual oxidation number for oxygen is -2. A common exception to this rule is hydrogen peroxide H2O2. In peroxides the oxidation number of oxygen is -1. What is the oxidation number of oxygen in H2O2?

-1

Assign oxidation numbers to each element in P2O5. The oxidation number for oxygen is -2 (rule 5). There is no rule that gives the oxidation number for phosphorus. Therefore, we must calculate it using the above equation. What oxidation number should we use for oxygen in the above equation?

-2

Assign oxidation numbers to each element in SO2. Using rule 7 we get; What is the oxidation number of oxygen in SO2?

-2

RULE 5: The usual oxidation number for oxygen is -2. Oxygen is in group VIA and will gain two electrons when reacting with a metal. Since oxygen wants to gain two electrons its charge will be -2. What is the oxidation number of oxygen in MgO?

-2

What is the oxidation number of oxygen in TiO2?

-2

Assign oxidation numbers to all elements in KMnO4: There is no rule which covers the oxidation number of manganese (Mn). What is the oxidation number of oxygen in KMnO4? (rule 5) Oxidation number of potassium in KMnO4? (rule 3)

-2, +1

Assign oxidation numbers to each element in SO2: What is the oxidation number of oxygen in SO2? What is the oxidation number of sulfur in SO2?

-2, +4

Calculate the oxidation number for sulfur in each compound. H2S = ___ SO2 = ___ SO3 = ___ SO42- = ___

-2, +4, +6, +6

Assign oxidation numbers to all elements in PO43- What is the oxidation number of oxygen in PO43-? What is the oxidation number of phosphorus in PO43-?

-2, +5

Assign oxidation numbers to each element in P2O5 What is the oxidation number of each oxygen in P2O5? What is the oxidation number of phosphorus in P2O5?

-2, +5

RULE 8: The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion must equal the charge on the ion. Applying this rule to PO43- says; What is the oxidation number for oxygen in PO43-? Is there a rule for the oxidation number of P? (yes, no)

-2, no

What is the oxidation number of N3-?

-3

Assign oxidation numbers to all elements in NH3. Nitrogen ox # ___ Hydrogen ox # ___

-3, +1

Assign oxidation numbers to all elements in NH3. Since NH3 is neutral, the sum of the oxidation numbers must equal what? ____

0

Assign oxidation numbers to each element in SO2. Since there is no rule covering sulfur we must use rule 7 to calculate sulfur's oxidation number. What is the charge on SO2?

0

RULE 1: The oxidation number of an atom in its elemental (uncombined) state is zero. For example, the oxidation number of Fe (iron) is 0. The oxidation number of As (arsenic) is also 0. What is the oxidation number for Hg?

0

RULE 1: The oxidation number of an atom in its elemental (uncombined) state is zero. The diatomic gases (H2, N2, O2, Cl2, etc) are considered to be in their elemental state. Since the diatomic gases are in their elemental state their oxidation number is 0. For example, the oxidation number of each oxygen in O2 is 0. What is the oxidation number of F in F2?

0

RULE 7: The algebraic sum of the oxidation numbers of all atoms in a neutral molecule must be zero. For example, P2O5 is a neutral molecule - it has no charge. Therefore, rule 7 says that the phosphorus oxidation numbers plus the oxygen oxidation numbers must equal zero. What is the charge on compound P2O5?

0

What is the oxidation number of N in N2?

0

STEP 1: Determine oxidation numbers for all elements involved in the reaction. Notice that sulfur and oxygen on the left side of this chemical equation are both in their elemental states. Therefore, their oxidation numbers are; S ox # ___ O ox # ___

0, 0

In each of these reactions magnesium loses two electrons to become a Mg2+ ion. The only difference in these reactions is the substance (i.e., O2, S, Cl2, and N2) that causes magnesium to lose its electrons. Magnesium loses HOW MANY electrons in each of these reactions?

2

In order for a chemical reaction to occur three conditions must be met by the atoms or molecules involved. 1. Reactant particles must collide with each other. 2. Colliding particles must impact with sufficient energy. 3. Reactant particles must collide with a specific orientation. How many conditions must be met for a reaction to occur?

3

Le Chatelier's principle states if a stress is applied to a system at equilibrium, the system will adjust in a direction to reduce the stress on the system. The word "stress" means a change in the (1) concentration, (2) pressure, or (3) temperature of the system at equilibrium. We will use this principle to predict how these changes affect the reaction direction. How many different types of changes will be considered?

3

Once we know the value of the equilibrium constant, it can be used to answer three important questions: 1. Determining whether a particular reaction favors products or reactants. 2. Predicting the reaction direction of a mixture that is not at equilibrium. 3. Determining the equilibrium composition for any set of starting concentrations. Which of the above is a "quantitative" determination?

3

The modern definition of OXIDATION and REDUCTION does not just apply to the gain or loss of oxygen. Current definitions include changes produced in substances by compounds that do not contain oxygen. Oxidation occurs in all of the following reactions: How many of these reactions DO NOT involve oxygen?

3

REACTION RATE is how fast reactants change into products. The rate of a chemical reaction depends on a number of factors. We encounter the most important ones frequently. The most important factors affecting the reaction rate are: 1. Physical nature of the reactants 2. Temperature 3. Concentration of the reactants 4. Catalyst How many factors affect the rate of a chemical reaction?

4

There are four steps to determine which substances in a chemical reaction are the oxidizing and reducing agents. 1. Determine oxidation numbers for all elements involved in the reaction. 2. Compare oxidation numbers of elements on left and right sides of the equation. 3. Determine substance oxidized and substance reduced. 4. Determine reducing and oxidizing agents. How many steps are there in determining oxidizing/reducing agents?

4

RULE 7: The algebraic sum of the oxidation numbers of all atoms in a neutral molecule must be zero. Applying this rule to P2O5 says: Which rule gives the oxidation number for oxygen?

5

Assign oxidation numbers to all elements in KMnO4. What rule should we use to calculate oxidation numbers since KMnO4 is a neutral molecule?

7

Each atom in a formula is associated with its own oxidation number. The oxidation numbers for the individual atoms are calculated using a standard set of rules. The rules used to calculate oxidation numbers are shown above. You will find that many of these rules correspond to the ionic charges we used for determining formulas of ionic compounds. However, there are exceptions which make drastic changes for the oxidation number on many elements. How many rules are there for calculating oxidation numbers?

8

Consider the original definition of oxidation - gain of oxygen. Which substance is oxidized in this reaction?

Al

Since carbon is causing water to be reduced it is a REDUCING AGENT. However, carbon is OXIDIZED because it gains oxygen. Which substance is oxidized? _______ Which substance is the reducing agent? _______ (Hint: use chemical formula)

C, C

Consider the original definitions for oxidation and reduction. What substance is oxidized? _______ What substance is reduced? _______

C, Fe2O3

Consider the original definitions for oxidation and reduction. What substance is oxidized? ______ What substance is reduced? ______

CO, Fe2O3

What substance is oxidized? _______ What substance is reduced? _______ What substance is the reducing agent? _______ What substance is the oxidizing agent? _______

CO, Fe2O3, CO, Fe2O3

Consider the original definition of reduction - loss of oxygen. Which substance is reduced in this reaction?

CuO

Consider the original definitions for oxidation and reduction. What substance is oxidized? ______ What substance is reduced? ______

H2, CuO

Since water is causing carbon to be oxidized it is an OXIDIZING AGENT. However, water is REDUCED because it loses oxygen. Which substance is reduced? ______ Which substance is the oxidizing agent? ______ (Hint: use chemical formula)

H2O, H2O

For the purpose of this excercise for typing in your answer, a general equilibrium reaction is given:The equilibrium expression can be typed as follows: Kc = [B]^2/[A] Following the format above, write the equilibrium expression for the reaction:

Kc= [H2O]^2/[H2]^2[O2]

An equilibrium constant expression is defined in terms of the balanced chemical equation. For the purpose of this excercise for typing in your answer, a general equilibrium reaction is given:The equilibrium expression can be typed as follows: Kc = [B]^2/[A] Following the format above, write the equilibrium expression for the reaction:

Kc= [NO2]^2/[N2O4]

Following the format given previously for writing a equilibrium expression, write the equilibrium expression for the reaction:

Kc=[O2]^3/[O3]^2

Symbol of the element oxidized ___ Symbol of the element reduced ___ Substance that is the oxidizing agent ____ Substance that is the reducing agent ____

N, O, O2, NH3

Consider the original definition of oxidation - gain of oxygen. Which substance is oxidized in this reaction?

NO

• Oxidized - the substance that INCREASES in oxidation number. • Reduced - the substance that DECREASES in oxidation number. (a) Cl (b) Cl- Comparing the above atoms; Which chlorine is in the oxidized state? ____ Which chlorine is in the reduced state? ____

a, b

All chemical reactions have an activation energy. The chemical reactants must have enough energy to reach the top of the "activation hill" before products can form. When only a few particles have sufficient energy to reach the top of activation hill, the reaction goes slow or not at all. There is an __________ __________ for all chemical reactions.

activation energy

Many times the particles just bounce off each other when they collide. As two atoms get closer, repulsion builds up between the negatively charged electrons. If the atoms DO NOT have high enough kinetic energy (speed) to over come the repulsion, they never get close enough to react. The minimum kinetic energy needed for a reaction to occur is called the ACTIVATION ENERGY - as seen in the figure below. The minimum energy needed for a reaction to occur is the ________ _________.

activation energy

• Oxidized - the substance that INCREASES in oxidation number. • Reduced - the substance that DECREASES in oxidation number. (a) N3- (b) N5+ Which nitrogen is in the oxidized state? ___ Which nitrogen is in the reduced state? ___

b, a

• Oxidized - the substance that INCREASES in oxidation number. • Reduced - the substance that DECREASES in oxidation number. (a) Na0 (b) Na+ Comparing the above atoms: Which sodium is in the oxidized state, (a or b) ? ____ Which sodium is in the reduced state (a or b) ? ____ (Hint: use letter a or b for your answer)

b, a

• Oxidized - the substance that INCREASES in oxidation number. • Reduced - the substance that DECREASES in oxidation number. (a) Fe2+ (b) Fe3+ Comparing the above atoms; Which iron has the greatest oxidization number? ___ Which iron is in the oxidized state? ___ Which iron is in the reduced state? ___

b, b, a

An oxidation-reduction reaction occurs whenever there is a transfer of e_________.

electrons

The OXIDATION NUMBER is the charge that an individual atom appears to have in a chemical compound. Oxidation numbers are calculated according to rules rather than being actual charges on the atoms. This is why the definition uses the phrase "appears to have." Oxidation numbers are (calculated, actual) charges on the atoms.

calculated

A substance that speeds up a chemical reaction without being consumed in the reaction is called a ________.

catalyst

Chemical equilibrium represents a delicate balance between forward and reverse reactions. A change in the reaction conditions may disturb the balance. If this occurs, the equilibrium position will shift to find a new state of balance. For example, we have seen that the equilibrium constant depends on the temperature of the reaction. Changing the temperature of a reaction will (change, not change) the equilibrium position.

change

Chemical reactions can be fast or slow. Chemical kinetics is the area of chemistry concerned with the speed, or rate, at which a chemical reaction occurs. The word "kinetic" suggests movement or change. Therefore, chemical kinetics evaluates the factors which effect the speed at which reactants change into products during a chemical reaction. The area of chemistry which studies the speed of chemical reactions is called _____ ____.

chemical kinetics

Corrosion is defined as the atmospheric oxidation of metals. By far the most important form of corrosion is the rusting of iron. Rusting is essentially a process of oxidation in which iron combines with water and oxygen to form rust, the reddish-brown crust that forms on the surface of iron. Rust is a chemical compound, a hydrated iron (III) oxide (Fe2O3⋅H2O). The chemical reaction of rusting involves the oxidation of metallic iron to ferrous ion (Fe2+) and the oxidation of the ferrous ion with oxygen and water to form ferric iron (Fe3+) rust. The reaction is catalyzed by water, salts and acids. Chemical reactions always produce new substances. Both the chemical and physical properties of the substances involved in the chemical reaction are changed. Oxygen reacts with iron to produce iron (III) oxide (rust). Iron is a metal and oxygen is an invisible gas. The chemical reaction produces a dull-red powder. This material has physical and chemical properties very different from the starting elements. A new substance is always produced in a _______ ______.

chemical reaction

Since chemical reactions always produce new substances, both the chemical and physical properties of the substances involved in the reaction are changed. For example oxygen reacts with iron to produce iron oxide (rust). Iron is a metal and oxygen is an invisible gas. The chemical reaction produces a dull-red powder. This material has physical and chemical properties very different from the starting elements. A new substance is always produced in a _______ ______.

chemical reaction

The values of the reactant and product concentrations are used to calculate the equilibrium constant for the reaction. Consider the general reaction: where a, b, d, and e are coefficients in the balanced chemical equation. The equilibrium constant for this reaction is given by the equation: In the expression for the equilibrium constant, the values of a, b, d, and e are the c____ for the balanced chemical equation.

coefficients

The first condition for a reaction to occur states that particles must ________.

collide

Most chemical reactions occur in the liquid or gas phase. This fact is explained by the concept of particle collisions. For COLLISIONS to occur the particles must be moving. We have seen that particles in solids are held in rigid patterns and are not free to move about. Only in liquids and gases do particles move around freely. Atoms, molecules, or ions must be moving for a ________ to occur.

collision

RULE 3: The oxidation numbers of groups IA and IIA elements when combined in a compound are always +1 and +2 respectively. Rule 3 only applies to elements when combined in compounds. Remember in the elemental state atoms have zero oxidation numbers. A group IA or IIA element must be in a _______ for rule 3 to apply.

compound

Equilibrium is a condition in which two opposing chemical reactions occur simultaneously at the same rate. Consider the elementary reaction A → B, for reactants A and products B, equilibrium is established when the concentrations of reactants and products remain constant, but are not equal as illustrated in the figure below. Thus, at equilibrium, the concentration of reactants and products remain __________.

constant

A pressure cooker increases the temperature at which water boils which increases the rate at which the food cooks. Likewise, keeping foods cold decreases the reaction rates which cause them to spoil. For example, the bacterial reactions that cause food to spoil proceed much more rapidly at room temperature than at the lower temperatures of a refrigerator. Keeping milk in a refrigerator will (increase, decrease) the rate at which it will go sour.

decrease

Le Chatelier's principle indicates the shift in the equilibrium position that results from a pressure change caused by a change in volume. For example, increasing the pressure of a system at equilibrium will cause the system to shift in a direction that reduces the total number of gas molecules. Decreasing the volume of a gaseous system at equilibrium will cause the system to (increase, decrease) the total number of gas molecules.

decrease

The most important factors affecting the reaction rate are: 1. Physical nature of the reactants 2. Temperature 3. Concentration of the reactants 4. Catalyst Increasing the concentration of reactants increases the reaction rate. High concentrations have more molecules in the same volume. More collisions occur between reactant molecules when their concentration is higher. Increasing the number of collisions will increase the reaction rate. Decreasing the concentration of reactants will (increase, decrease) the number of collisions between molecules.

decrease

The most important factors affecting the reaction rate are: 1. Physical nature of the reactants 2. Temperature 3. Concentration of the reactants 4. Catalyst Increasing the temperature usually increases the reaction rate. The reaction rate will (increase, decrease) when the temperature is lowered.

decrease

• Oxidized - the substance that INCREASES in oxidation number. • Reduced - the substance that DECREASES in oxidation number. A substance's oxidation number will (increase, decrease) when it is reduced.

decrease

A catalyst lowers the activation energy for the reaction by providing a different path for the reactants to combine. A lower activation energy means that more molecules can make it to the top of the activation barrier and react. The activation energy of a reaction is (increased, decreased) by the presence of a catalyst.

decreased

During hibernation the body temperature of animals decreases. When a woodchuck hibernates its body temperature drops almost to freezing. In this condition its body functions almost stops. An active woodchuck's heartbeat is 80 times a minute while a hibernating woodchuck's heartbeat may only be 4 times a minute. Although their body functions are very slow, a woodchuck may lose 40 percent of its body weight during the winter. A hibernating animal needs less oxygen because its body temperature (increases, decreases).

decreases

STEP 2: Compare oxidation numbers of elements on left and right sides of the equation. Fe in FeO (increases, decreases, same). O in FeO (increases, decreases, same). C in C (increases, decreases, same).

decreases, same, increases

The equilibrium constant for this reaction is given by the equation: The equilibrium constant expression implies the following 1. Products concentrations are always in the numerator 2. Reactant concentrations are always in the denominator 3. The concentrations of the reactants and products are raised to a power equal to their coefficient in the balanced chemical equation. The equilibrium constant expression has reactants in the d______ and the products in the n_____ .

denominator, numerator

Consider the reaction A → B, in which we start with pure compound A in a closed container. As [A] decreases the rate of the forward reaction, Kf, decreases. Likewise, as [B] increases the rate of the reverse reaction, Kr, increases. Eventually the reaction reaches a point at which the forward (Kf) and reverse (Kr) rates become equal, and the concentrations of A and B no longer change (composition remains constant) and the ratio [B]/[A] = a constant At equilibrium the concentrations of reactants and products (do, do not) change with time.

do not

Because the oxidation number for hydrogen does not change, it is neither oxidized or reduced in this reaction. Every element (does, does not) change oxidation number.

does not

We have been discussing the effect of concentration changes on a system at equilibrium. If we add a pure solid to an equilibrium system there is no shift in the equilibrium position. This is because there is no change in the concentration. The solid is 100% pure before the addition and it is still 100% after the addition. An equilibrium system involving a pure solid (does, does not) shift when more solid is added.

does not

We have already seen examples of equilibrium. The vapor pressure of water in a closed bottle is one example as shown in the figure above. Equilibrium is established when the rate at which liquid water evaporates equals the rate at which the gaseous water condenses. Equilibrium is a dynamic process since both evaporation and condensation are occurring at equal rates. (Note: For equilibrium to occur neither reactants nor products can be allowed to escape the container - the change must be in a closed system) Equilibrium is a (static, dynamic) process.

dynamic

Since heat is lost by an exothermic process or gained by an endothermic process, heat can be considered a reactant or product in a chemical or physical change. If a chemical reaction gets cold, the reaction is (exothermic, endothermic)

endothermic

Temperature has a significant effect on most reactions. For example consider the equilibrium when CoCl2 is dissolved in HCl (hydrochloric acid): The photograph above shows that at high temperature the blueform of cobalt is favored while at low temperature the pink form of cobalt is favored. The above reaction is (endothermic, exothermic).

endothermic

The second condition for a reaction to occur states that particles must collide with sufficient _________.

energy

Catalysts are extremely important for living things to function properly including the human body. Enzymes are biological catalysts. They cause many reactions in the body to take place under mild conditions of body temperature. Without these enzymes (catalysts), digestion of food would take weeks not hours. Biological catalysts are known as _______.

enzymes

Most chemical reactions reach a steady-state condition and appear to stop before they reach completion. When this condition occurs there are actually two reactions occurring: (1) a forward reaction which consumes reactants to form products, and (2) a reverse reaction which consumes the products to re-form the reactants. Equilibrium is achieved when the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant. For chemical equilibrium to occur a forward reaction rate must be ____ to a ______ reaction rate.

equal, reverse

Exothermic process are chemical or physical changes in which heat is evolved. Endothermic process are chemical or physical changes in which heat is absorbed. The system is defined as the materials undergoing a process. If a process is exothermic the system produces heat so thermal energy is transferred from the system to the surroundings. If a process is endothermic the system absorbs heat so thermal energy is transferred from the surroundings to the system. Note: you look for the change of heat in the surroundings as shown in the figure below. If the surroundings gain heat, the system will be (exothermic, endothermic).

exothermic

Consider the general reaction: The equilibrium constant for this reaction is given by the equation: We call this equation the equilibrium constant expression. The equilibrium constant Kc is determined by substituting the actual equilibrium concentrations into the expression. The subscript "c" on the Kc indicates that concentrations (in molarity) are used. The value Kc is determined by the equilibrium constant _____ .

expression

As shown in the figure below, the minimum kinetic energy needed for a reaction to occur is called the ACTIVATION ENERGY. Every chemical reaction has a unique activation energy. The activation energy is one of the main factors that determines how fast a reaction proceeds. Reactions with high-activation energies are slow; reactions with low-activation energies are fast. All chemical reactions have the same activation energy. (true, false)

false

It is common to assume that chemical reactions go to completion, that is, reactions continue until one or more of the reactants is completely used up. However, this usually is not the case. For most chemical reactions, the complete conversion of reactants to products does not occur regardless of the amount of time allowed for the reaction. The reason for this is that product molecules can react with each other to re-form the reactants. With time the rate of product formation and the rate of reactant re-formation become equal which results in a steady-state condition. At this point the reaction appears to stop because the concentrations of the reactants and products remain constant. Most reactions go to completion. (true, false)

false

A charcoal briquette can take several hours to burn. However, if you grind the charcoal briquette into a fine powder it will burn dangerously fast. To completely describe a chemical reaction we need to know how fast the reactants change into products. It is important for us to know how ____ a chemical reaction will occur.

fast

Small particles react faster than larger particles. If the particle size is very small, reaction rates can be so fast that an explosion occurs. A large lump of coal burns slowly in air. However, coal dust in underground coal mines is very dangerous because it burns explosively fast. Saw dust is dangerous because it has high surface area and will burn (fast, slow).

fast

Catalysts decrease the activation energy of a reaction. When the activation energy is lower, the rate of a chemical reaction will be (faster, slower).

faster

If the reactant is a solid, the physical nature also depends on the particle size. Reactions occur at the surface of solids. Decreasing the particle size increases the amount of surface (surface area) which increases the reaction rate. For example, you cannot start a large log on fire with a match, but you can start a pile of small twigs on fire because they are smaller and have high surface area. Small particles react (faster, slower) than larger particles.

faster

In summary; if the pressure of a gaseous reaction mixture is increased by decreasing the volume, the reaction will shift in direction which gives fewer gas molecules. Consider the reaction: If the pressure of this mixture is increased by reducing the volume it responds by shifting in a direction which gives fewer gaseous molecules. In this case the reaction shifts to the left, since there are fewer moles of gaseous reactants. When NO2 reacts to give N2O4 there will be (fewer, more) gaseous molecules.

fewer

Chemical equilibrium is a condition in which two opposing chemical reactions occur simultaneously at the same rate. Consider the elementary reaction A → B, the forward and reverse reactions are: Forward reaction: A → B rate forward Reverse reaction: B → A rate reverse As shown in the figure above, equilibrium is established when the rates of the forward and reverse reactions are equal. Thus, at equilibrium the f_____ reaction rate equals the r_____ reaction rate.

forward, reverse

A car engine does not run when it is flooded. This is because liquid gasoline is in the engine and not gaseous gasoline. A car engine requires the gasoline to be in the (liquid, gaseous) state before it can run.

gaseous

Solids do react but usually only on their surfaces where a liquid or gas particle can collide. Thus, only a small fraction of the solid particles can react at any time. Solids are most likely to react with (solid, gaseous) particles.

gaseous

The physical state "solid, liquid, gas" of the reactants affects the reaction rate. Reaction rate order is: gases > liquids > solids Gases react the fastest because their particles are moving the fastest with the highest kinetic energy which gives the most collisions between the reactants. Which physical state reacts the fastest? _______ Which physical state reacts the slowest? _______

gases, solids

If a reaction is exothermic the temperature of the surroundings will (increase, decrease)

increase

Increasing the temperature will _______ the rate of a chemical reaction.

increase

Le Chatelier's principle indicates the shift in the equilibrium position that results from a pressure caused by a change in volume. For example, decreasing the pressure of a system at equilibrium will cause the system to shift in a direction that increases the total number of gas molecules. Increasing the volume of a system at equilibrium will cause the system to (increase, decrease) the total number of gas molecules.

increase

The following rules apply when determining which substance is oxidized and which substance is reduced; • Oxidized - the substance that INCREASES in oxidation number. • Reduced - the substance that DECREASES in oxidation number. A substance's oxidation number will (increase, decrease) when it is oxidized.

increase

The most important factors affecting the reaction rate are: 1. Physical nature of the reactants 2. Temperature 3. Concentration of the reactants 4. Catalyst A catalyst will increase the rate of a chemical reaction. The reaction rate will (increase, decrease) when a catalyst is present.

increase

The most important factors affecting the reaction rate are: 1. Physical nature of the reactants 2. Temperature 3. Concentration of the reactants 4. Catalyst Increasing the temperature usually increases the reaction rate. Increasing the temperature increases the kinetic energy or speed of the particles. Therefore, molecules at high temperature move faster than they do at low temperatures. When the reactant molecules move faster they have more collisions which increases the reaction rate. At room temperature, the rates of many chemical reactions will DOUBLE when the temperature is increased by 10oC. Increasing the temperature will (increase, decrease) the number of collisions between reactant molecules.

increase

Consider the reaction: STEP 2: Compare oxidation numbers of elements on left and right sides of the equation. Sulfur's oxidation number (increases, decreases). Oxygen's oxidation number (increases, decreases).

increases, decreases

STEP 2: Compare oxidation numbers of elements on left and right sides of the equation. Carbon's (in CO) oxidation number (increases, decreases, same). Oxygen's (in CO) oxidation number (increases, decreases, same). Oxygen's (for O2) oxidation number (increases, decreases, same).

increases, same, decreases

Wood burns much faster in pure oxygen than it does in air. (Air is only 21 percent oxygen). Blowing on a fire causes it to burn faster. By blowing on a fire you are (increasing, decreasing) the concentration of oxygen.

increasing

Consider the equilibrium mixture: A decrease in the I2 concentration will cause the reaction to shift to the (left, right).

left

Consider the equilibrium mixture: If additional HI is added to the reaction mixture the concentration of HI will increase. Le Chatelier's principle predicts that the reaction will shift to reduce this increase in concentration. Thus, some of the HI will decompose to form H2 and I2. An increase in the HI concentration will cause the reaction to shift to the (left, right).

left

For the above reaction, an increase in pressure will decrease the volume, and will shift the reaction to the (left, right).

left

Just like gases, changing the concentration of dissolved aqueous species will change the equilibrium position of an aqueous system. Consider a saturated solution of silver chloride; Because HCl is a strong acid, the addition of HCl will increase the concentration of Cl-. If HCl is added to the above reaction, which direction (left, right) will the reaction shift?

left

In what direction (left, right) will the equilibrium shift when (a) Cl2 is added (b) temperature is increased (c) PCl5 is added (d) volume is decreased

left, right, right, left

Consider a saturated solution of silver chloride; The addition of HCl will increase the concentration of Cl- which will shift the equilibrium position to left. When the above reaction shifts to the left, silver chloride becomes (less, more) soluble.

less

Chemical reactions or physical changes are either exothermic or endothermic processes as shown in the figure below: - Exothermic process are chemical or physical changes in which heat is evolved. - Endothermic process are chemical or physical changes in which heat is absorbed. An exothermic process will (gain, lose) heat. An endothermic process will (gain, lose) heat.

lose, gain

The pressure of a system will increase if its volume is decreased. Le Chatelier's principle indicates that the system will respond by shifting its equilibrium position to reduce the increase in pressure. A system can reduce its pressure by reducing the total number of gas molecules. A reduction in the number of gas molecules will produce a (lower, higher) pressure.

lower

Body functions require 13% more oxygen for every 1oC increase in body temperature. Decreasing the body temperature decreases the amount of oxygen needed for body functions. During open-heart surgery, a patient's body temperature is lowered 2-3oC to decrease the amount of oxygen needed by the body during the operation. The body uses (more, less) oxygen when its temperature increases.

more

Consider a saturated solution of silver chloride; If you remove Ag+ from the above system, the silver chloride will become (less, more) soluble.

more

For a reaction to occur, reactant particles must collide with a specific orientation. Consider the following reaction between molecules AB and CD: In this reaction, B and C exchange places to produce molecules AC and BD. Since B and C exchange places, the most favorable orientation would put A close to C and B close to D. This orientation is shown in Figure (a) below. As shown in (a) above, a reaction is (less, more) probable when A and C, and B and D are simultaneously close together.

more

An equilibrium system involving a pure solid does not shift if more solid is added. In general, adding or removing a species disturbs the equilibrium system only when the concentration of the species appears in the equilibrium expression. For example, consider the decomposition of calcium carbonate; Will adding or removing CaCO3 or CaO change the equilibrium position of the above reaction? (yes, no)

no

As shown in the figure below, the concentrations of reactants and products remain constant in a system at equilibrium. These constant values of the reactant and product concentrations are used to calculate an equilibrium constant for the reaction. At a fixed temperature, the equilibrium constant is a single number which describes the extent to which a chemical reaction can occur. At a fixed temperature, does the equilibrium constant for a reaction change? (no, yes)

no

Assign oxidation numbers to each element in SO2. There is a rule for the oxidation number of oxygen. Is there a rule for the oxidation number of sulfur? (yes, no)

no

Consider the the dissolving of solid lead chloride in water; Will adding or removing PbCl2 change the equilibrium position of the above reaction? (yes, no)

no

For reactions which have no change in number of gaseous molecules, a pressure change has no effect on the equilibrium. For example; has no change in the moles of gaseous molecules; there are 2 moles of gaseous reactants and 2 moles of gaseous products. Will a pressure change in the above reaction cause a shift in the equilibrium position? (yes, no)

no

For the reaction A → B at equilibrium, [B]/[A] = a constant (note: square brackets mean that concentrations have molarity units). It makes no difference whether we start with pure A or pure B or even a mixture of A and B. At equilibrium the ratio of the product and reactant concentrations is always equal to a constant value. Does the ratio of the product and reactant concentrations change for a reaction at equilibrium? (no, yes)

no

Is this reaction a redox reaction? (yes, no)?

no

It is important to note that only pressure changes caused by a volume change will affect the equilibrium position of a reaction. Pressure may be increased by the addition of a non-reacting gas, such as argon, to a reaction vessel. However, the addition does not alter the partial pressures of the gaseous mixture and therefore does not cause a shift in the equilibrium position. Will the addition of an inert gas cause a reaction to shift its equilibrium position? (yes, no)

no

Many industrial processes require rare and expensive metal catalysts. The production of gasoline from crude oil and the production of most fertilizers require platinum catalysts. It is practical to use these expensive catalysts because they are not consumed in the reaction and can be used over and over. Are catalysts consumed in a chemical reaction? (yes, no)

no

Not all reactions are Redox (oxidation-reduction) reactions. To be a redox reaction there needs to be an oxidizing agent and a reducing agent. In other words, something must be oxidized and something must be reduced. Are all reactions oxidation-reduction reactions? (yes, no)

no

Occasionally, reactions speed up when a substance other than one of the reactants is added to the mixture. These substances are called catalysts. A catalyst is a substance that increases the rate of a chemical reaction but does not get consumed by the reaction. Is a catalyst consumed in a chemical reaction? (yes, no)

no

Oxidation and reduction processes ALWAYS occur together. You cannot have oxidation without reduction. If electrons are lost by one substance another substance has to gain the electrons. Electrons just don't disappear. Can oxidation occur without reduction? (yes, no)

no

The oxidation number of oxygen remains the same on both sides of the equation when comparing the oxidation number of oxygen in CO with that of the oxidation number of oxygen in CO2 (-2 and -2). Has the oxygen in CO been oxidized or reduced? (yes, no)

no

We know that a catalyst increases the rate of a reaction. However, a catalyst does not change the equilibrium constant. This is understood when we remember that a catalyst lowers the activation energy of a reaction. The activation energy is lowered for the forward reaction but so is the activation energy for the reverse reaction. Thus, a catalyst speeds up the forward reaction and reverse reactions and therefore has no effect on the equilibrium constant. Does a catalyst affect the position of the equilibrium constant for a reaction? (yes, no)

no

You cannot predict how much the reaction rate will increase when the concentration is increased. The reaction rate usually increases but not to the same extent for different reactions. Sometimes the rate will double when the concentration is doubled but other times it may be more or it may be less. For example, steel wool burns with difficulty in air, which contains 20% oxygen, but bursts into a brilliant white flame in pure oxygen. Will the reaction rate for all chemical reactions increase the same amount when the concentration of reactants is increased? (yes, no)

no

For the above reaction, an increase in pressure results in decreased volume, andwill shift the reaction to the: (left, right, no change).

no change

This is an acid-base neutralization reaction; not a redox reaction. Is hydrogen or chloride in HCl reduced or oxidized? (yes, no) Is the sodium or hydroxide in NaOH reduced or oxidized? (yes, no)

no, no

For the reaction A → B at equilibrium it makes no difference whether we start with pure A or pure B or even a mixture of A and B. At equilibrium the ratio of the product and reactant concentrations is always equal to a constant value. Suppose we start with pure compound A in a closed container. As A reacts to form B, the concentration of A decreases and the concentration of B increases as shown in figure (a) below. As [A] decreases the rate of the forward reaction, Kf, decreases. Likewise, as [B] increase the rate of the reverse reaction, Kr, increases. These rate changes, Kf and Kr, are shown in figure (b). Do the concentrations [A] and [B] become equal? (no, yes) Do the forward rate Kf and the reverse rate Kr become equal? (no, yes)

no, yes

RULE 4: The oxidation number of fluorine in all compounds is -1 and for other group VII elements in compounds it is usually -1. For example, the oxidation number of F in NaF is -1. The oxidation number of Cl in CaCl2 is -1. Can fluorine have an oxidation number different than -1? (yes, no) Can chlorine have an oxidation number different than -1? (yes, no)

no, yes

Lets review what the equilibrium constant expression implies: 1. Products concentrations are always in the n_____ 2. Reactant concentrations are always in the d_____ 3. The concentrations of the reactants and products are always raised to a p_____ equal to their coefficient in the balanced chemical equation

numerator, denominator, power

An OXIDATION NUMBER is the charge that an individual atom appears to have in a chemical compound. Oxidation numbers are used to help determine: 1. If the reaction is an oxidation-reduction reaction. 2. Which substances are oxidized or reduced. Each atom in a chemical formula will have an ________ number.

oxidation

The phrase oxidation-reduction reaction is often shortened to REDOX reaction. • Thus, redox means oxidation-reduction. A redox reaction is an o______- r______ reaction.

oxidation reduction

Let's compare the definitions of oxidation and reduction. • OXIDATION is the LOSS of electrons or OXIDATION is the GAIN of oxygen. • REDUCTION is the GAIN of electrons or REDUCTION is the LOSS of oxygen. Loss of electrons is ________. Loss of oxygen is ______.

oxidation, reduction

Oxidation and reduction processes ALWAYS occur together. When one substance loses electrons another substance must gain the electrons. Electron transfer forms the basis for o____ - r____ reactions.

oxidation, reduction

The modern definitions for OXIDATION and REDUCTION involve the loss or gain of electrons. • OXIDATION is the LOSS of electrons. • REDUCTION is the GAIN of electrons. The loss of electrons is ______. The gain of electrons is ______.

oxidation, reduction

The original definitions of OXIDATION and REDUCTION were: • OXIDATION is the GAIN of oxygen. • REDUCTION is the LOSS of oxygen. The gain of oxygen is ______. The loss of oxygen is ______.

oxidation, reduction

OXIDATION-REDUCTION reactions are a very common and important type of reaction. These reactions occur when -energy is obtained from food -batteries produce electricity -iron corrodes or rusts -antiseptic agents kill bacteria -iron, copper, and aluminum are made -when natural gas is burned to heat a house What type of reactions are these?

oxidation-reduction

CuO is reduced because it loses oxygen. However, hydrogen gains oxygen in this reaction. Hydrogen (H2) is (oxidized, reduced)

oxidized

According to the original definition of oxidation - gain of oxygen, hydrogen (H2) has been oxidized in this reaction. When a substance gains oxygen it is (oxidized, reduced). When a substance loses oxygen it is (oxidized, reduced).

oxidized, reduced

An easy way to remember which substances are the oxidizing and reducing agents is the following relationship. • Substance oxidized = Reducing agent • Substance reduced = Oxidizing agent You should determine the oxidized and reduced substances first when determining the oxidizing and reducing agents in a reaction. The reducing agent is always (oxidized, reduced). The oxidizing agent is always (oxidized, reduced).

oxidized, reduced

Consider the reaction: STEP 3: Determine substance oxidized and substance reduced. Sulfur is (oxidized, reduced). Oxygen is (oxidized, reduced).

oxidized, reduced

STEP 3: Determine substance oxidized and substance reduced. Carbon is (oxidized, reduced). Oxygen (from O2) is (oxidized, reduced).

oxidized, reduced

The terms OXIDIZED and REDUCED always apply to the reactants in an equation. • The substance OXIDIZED loses electrons or gains oxygen. • The substance REDUCED gains electrons or loses oxygen. Reactants that lose electrons are said to be _______. Reactants that gain electrons are said to be _______.

oxidized, reduced

An OXIDIZING AGENT is a substance that causes another reactant to be oxidized. For example consider the reaction; Water is causing carbon to be oxidized because the carbon is gaining oxygen from the water. Thus, water is the oxidizing agent. A substance that causes the oxidation of another substance is an ______ agent.

oxidizing

If CO2 is reduced it will be the (oxidizing, reducing) agent.

oxidizing

STEP 4: Determine reducing and oxidizing agents. FeO is reduced; therefore it is the (oxidizing, reducing) agent. C is oxidized; therefore it is the (oxidizing, reducing) agent.

oxidizing, reducing

The terms OXIDATION and REDUCTION have several definitions. The term OXIDATION was first defined as the gain of oxygen. For example, consider the reactions: What common REACTANT (element name) is found in each of these reactions?

oxygen

Equilibrium between two phases of the same substance is called physical equilibrium because the changes that occur are only physical. The vaporization of water in a closed container at a given temperature is an example of physical equilibrium. The study of physical equilibrium yields useful information such as the relationship of vapor pressure to temperature. Vapor pressure is an example of p____ equilibrium

physical

Equilibrium between two phases of the same substance is called physical equilibrium. Chemical changes can also reach equilibrium. The same conditions which influence physical equilibrium also influence chemical equilibrium. Chemical equilibrium is a condition in which two opposing chemical reactions occur simultaneously at the same rate. Chemical equilibria are of great importance in understanding natural, environmental, and industrial processes. In this chapter we will see how to express the equilibrium position of a reaction and how to quantitatively determine the amounts of reactants and products that are present when a reaction is at equilibrium. Physical equilibrium involves _____ changes. Chemical equilibrium involves _____ changes.

physical, chemical

Heat is a (reactant, product) in an exothermic reaction.

product

An equilibrium constant can be used to qualitatively determine whether a particular reaction favors products or reactants. A large value of K (greater than 103) means that the numerical value of the numerator is significantly greater than the denominator. In terms of reactants and products, this means that the concentrations of products is greater than the reactants. Therefore, the equilibrium lies to the right and the products are favored. A large value of K favors p_____.

products

High pressure will favor (reactants, products) in this reaction..

products

Le Chatelier's principle can predict the effect of temperature changes on a reaction at equilibrium. Consider the equilibrium when CoCl2 is dissolved in HCl: Heat is consumed when this reaction proceeds to the right. Thus, if we add heat to the reaction (make it hot) it will shift to the right in an attempt to use up the heat. Heating an endothermic reaction will favor (products, reactants)

products

The reaction: has a Kc = 4.0x1013 at 25oC. The equilibrium reaction mixture will contain predominantly (reactants, products).

products

A reaction is less probable when molecules collide without the PROPER orientation. For a reaction to occur the particles must collide with the ________ orientation.

proper

The third condition for a reaction to occur states that particles must collide with (proper, any) orientation.

proper

Le Chatelier's principle gives qualitative predictions about the direction a reaction will shift as a result of a change in reaction conditions. Le Chatelier's principle states if a stress (change in conditions) is applied to a system at equilibrium, the system will adjust (change the equilibrium position) in a direction to reduce the stress on the system. Le Chatelier's principle gives (quantitative, qualitative) predictions about changes in reaction conditions.

qualitative

Heat is a (reactant, product) in an endothermic reaction.

reactant

An equilibrium constant can be used to qualitatively determine whether a particular reaction favors products or reactants. If an equilibrium constant is small (less than 10-3) then the concentrations of reactants are greater than the products. Therefore, the equilibrium lies to the left and the reactants are favored. A small K favors r_____.

reactants

Changing the reaction conditions will change the equilibrium position of a reaction. If the change causes more products to form, the equilibrium position is said to shift to the right. Similarly, if more reactants form as a result of the change, the equilibrium position is said to shift to the left. A reaction that shifts to the left as a result of a change in conditions will produce more (products, reactants).

reactants

Cooling an endothermic reaction will favor (reactants, products).

reactants

High pressure will favor (reactants, products) in this reaction.

reactants

Le Chatelier's principle can predict the effect of temperature changes on a reaction at equilibrium. Heat is consumed by an endothermic reaction. Thus, if we remove heat from the reaction (make it cold) it will shift to the left in an attempt to produce more heat. Cooling an endothermic reaction will favor (products, reactants)

reactants

The reaction rate is how fast reactants change into products. Fast reactions might occur within seconds and slow reactions might take days or even years to reach completion. The speed at which reactants change into products is known as the _______ ____.

reaction rate

Chemical reactions break the bonds between reactant atoms and form new bonds between product atoms. In other words, a chemical reaction causes the atoms to rearrange with the formation of new bonds. During a chemical reaction, the atoms will ________ and form new ________.

rearrange, bonds

The term REDUCTION was first used to describe a reaction which removed oxygen from a substance. For example, consider the reactions: Because the metal oxides lose oxygen their molar mass is (reduced, increased).

reduced

STEP 3: Determine substance oxidized and substance reduced. Fe in FeO (oxidized, reduced, same). O in FeO (oxidized, reduced, same). C in C (oxidized, reduced, same).

reduced, same, oxidized

A REDUCING AGENT is a substance that causes another substance to be reduced. For example consider the reaction; Carbon is causing water to be reduced because the water is losing oxygen to the carbon. Thus, carbon is the reducing agent. A substance that causes the reduction of another substance is a ______ agent.

reducing

Consider the reaction: STEP 4: Determine reducing an oxidizing agents. Sulfur is the (oxidizing, reducing) agent. O2 is the (oxidizing, reducing) agent.

reducing, oxidizing

STEP 4: Determine reducing and oxidizing agents. CO is the (oxidizing, reducing) agent. O2 is the (oxidizing, reducing) agent.

reducing, oxidizing

The substance oxidized is the (oxidizing, reducing) agent. The substance reduced is the (oxidizing, reducing) agent.

reducing, oxidizing

Let's compare the definitions of oxidation and reduction. • OXIDATION is the LOSS of electrons or OXIDATION is the GAIN of oxygen. • REDUCTION is the GAIN of electrons or REDUCTION is the LOSS of oxygen. Gain of electrons is ________. Gain of oxygen is ______.

reduction, oxidation

Chemical equilibrium is a condition in which two opposing chemical reactions occur simultaneously at the same rate. The forward and reverse reactions are shown below for the reaction of chlorine gas with hydrogen gas produces HCl, hydrochloric acid. The equilibrium equation has two half-headed arrows pointing in opposite directions, which denote a chemical system at equilibrium, and the reaction is therefore reversible. When the half-headed arrow notation is used in an equation, it means that a reaction is r___________.

reversible

Equilibrium is established when the rate at which liquid water evaporates equals the rate at which the gaseous water condenses. At equilibrium both evaporation and condensation are occurring at equal rates. Both evaporation and its reverse process, condensation, are needed to establish equilibrium. Therefore, a process must be reversible for equilibrium to be established. Equilibrium is the result of a ______ process.

reversible

Let's review what we know about equilibrium: Equilibrium is rev___________ Equilibrium is dy___________ Equilibrium can only occur in a _____________ container Equilibrium takes t________ to establish. Equilibrium concentrations depend on the t________________

reversible, dynamic, closed, time, temperature

Adding or removing a substance involved in a reaction will cause a change in concentration. Le Chatelier's principle predicts that the reaction will shift in a direction that minimizes the change in concentration. For example, if a gaseous reactant is added to a system, the equilibrium will shift in a direction (right) that consumes some of the added reactant. Likewise, if a gaseous product is added to system, the equilibrium will shift in a direction (left) that consumes the added product. Increasing the concentration of a reactant will shift the equilibrium to the (left, right).

right

Consider the equilibrium mixture: If additional H2 is added to the reaction mixture the concentration of H2 will increase. Le Chatelier's principle predicts that the reaction will shift to reduce this increase in concentration. The production of more HI uses H2 which decreases the higher H2concentration. An increase in the H2 concentration will cause the reaction to shift to the (left, right).

right

Consider the reaction;If the pressure of this mixture is decreased by increasing the volume it responds by shifting in a direction which gives more gaseous molecules. In the above case, which direction will the reaction shift? (left, right)

right

Le Chatelier's principle can predict the effect of temperature changes on a reaction at equilibrium. A simple way to do this is to treat heat as a reactant or product. In an endothermic reaction heat is a reactant, whereas in an exothermic reaction heat is a product. Thus, when the temperature is increased the equilibrium position shifts in a direction that absorbs heat. Likewise, when the temperature is decreased the reaction shifts in a direction that produces heat. Cooling an exothermic reaction will shift the equilibrium position to the (left, right).

right

Le Chatelier's principle predicts that a reaction will shift in a direction that minimizes a change in concentration. For example, if the concentration of a gaseous reactant is decreased, the equilibrium will shift in a direction (left) that will produce more of the reactant. Likewise, if a the concentration of a gaseous product is reduced, the equilibrium will shift in a direction (right) that produces more of the product. Decreasing the concentration of a product in a reaction will shift the equilibrium to the (left, right).

right

The most important factors affecting the reaction rate are: 1. Physical Nature of the reactants 2. Temperature 3. Concentration of the reactants 4. Catalyst The physical nature refers to the physical state "solid, liquid, gas" of each reactant. A reactant's physical state can be s____, l____, or g___.

solid, liquid, gas

Three conditions must be met for a reaction to occur: 1. Reactant particles must collide with each other. 2. Colliding particles must impact with sufficient energy. 3. Reactant particles must collide with a specific orientation. Collisions do not always result in a reaction. Statement 3 says that particles must hit each other with a specific orientation. For a reaction to occur particles must collide with (specific, any) orientation.

specific

Three conditions must be met for a reaction to occur: 1. Reactant particles must collide with each other. 2. Colliding particles must impact with sufficient energy. 3. Reactant particles must collide with a specific orientation. Collisions do not always result in a reaction. Statement 2 says that particles must hit each other with sufficient energy. For a reaction to occur particles must collide with _______ energy.

sufficient

The melting of ice is an endothermic process. Ice (system) must absorb heat from the surroundings to melt. If you hold an ice cube in your hand (part of the surroundings) it feels cold. This is because the ice cube gains heat and your hand loses heat. Since your hand loses heat its temperature goes down and it feels cold. The effect of an endothermic or exothermic process is observed in the (system, surroundings).

surroundings

An increase in temperature usually increases the rate of a reaction. For example, increasing the water temperature causes an increase in its evaporation rate which increases the equilibrium vapor pressure of the water. Thus, the equilibrium vapor pressure depends on the temperature. Equilibrium concentrations depend on the t______.

temperature

At equilibrium both evaporation and condensation are occurring at equal rates. However, when water is first put in a closed container there are very few water vapor molecules present as illustrated above. Therefore, the rate of evaporation exceeds the rate of condensation. With time, more of the water evaporates and the number of vapor molecules increases. The increasing water vapor concentration causes an increase in the rate of condensation. Eventually, the rate of condensation becomes equal to the rate of evaporation. Thus, we see that equilibrium does not occur immediately but requires time to established. It takes ___ to establish equilibrium.

time

An equilibrium constant expression is defined in terms of the balanced chemical equation. For example, the reaction of nitrogen and hydrogen to produce ammonia is given by the chemical equation: The equilibrium expression for this reaction is: An equilibrium expression depends on the stoichiometry of the chemical equation. (true, false)

true

Figure (b) shown below illustrates AB and CD colliding with an orientation that DOES NOT produce the orientation for the reaction; The reason is that A is not close to C and B is not close to D. This shows that certain orientations will NOT produce a reaction. Reactions may not occur because the particles do not collide with the proper orientation. (true, false)

true

If an atom does not have a charge it is NOT an ion. (true, false)

true

This reaction is NOT a redox reaction. Notice that none of the oxidation numbers of the elements change; Na is +1 on both sides, Ag is +1 on both sides, N is +5 on both sides, and Cl is -1on both sides. Therefore, none of the elements are oxidized or reduced. To be an oxidation-reduction reaction something must be oxidized and something must be reduced. (true, false)

true

When a reaction involves two or more substances, the reactant particles (atoms, molecules, or ions) must come in contact before any chemical change can occur. For a chemical reaction between two molecules to happen the molecules must collide. (true, false)

true

When the equilibrium constant is neither large nor small neither reactants or products are favored. For example, when an equilibrium constant has a value between 103 and 10-3measurable amounts of both products and reactants are present in the equilibrium mixture. A reaction with K=10 will have significant amounts of both products and reactants. (true, false)

true

A catalyst does not change the equilibrium constant for a reaction. Therefore, the addition of a catalyst (will, will not) shift the equilibrium position of a reaction.

will not

A chemical reaction does not occur if the reactants do not have sufficient energy to reach the top of the activation hill (see figure below). For example, a match must be struck before it lights. The heat produced by striking a match against a rough surface provides the necessary energy the reactants need. Once the reaction starts, it produces excess energy (heat) to keep the reaction going. Do chemical reactants have to collide with sufficient energy for a reaction to proceed? (yes, no)

yes

Catalysts increase the reaction rate in several ways. Some catalysts provide a different path by forming "intermediate" compounds with the reactants. Other catalysts provide a surface on which the reactants can combine. Can a catalyst form an intermediate compound with the reactants? (yes, no)

yes

Do oxidation and reduction reactions always occur together? (yes, no)

yes

Enzymes are very sensitive to temperature. The enzymes can be destroyed or deactivated by small temperature changes. One of the dangers of having a high fever during an illness is that your enzymes may stop working. Is it important to control a fever during an illness? (yes, no)

yes

Fireworks produce brilliant splashes of color in a dark sky. These multicolor explosions are the products of chemical reactions. The five basic ingredients include (1) a fuel which allows the firework to burn; (2) an oxidizer which produces oxygen to support combustion of the fuel; (3) color producing chemicals; (4) a binder which holds the firework pellet together; and (5) a chlorine donor which provides chlorine to strengthen the color of the flame, which may also serve as the oxidizer. Red colors are the result of Strontium and Lithium salts; Orange from Calcium salts; Yellow from Sodium salts; Green from Barium salts; Blue from Copper halides; White from Titanium, Aluminum and Magnesium metals. Colorful fireworks are the products of chemical reactions. However, chemical reactions occur all around us all the time and not just in dramatic reactions like explosions. In this unit we will learn what makes chemical reactions occur. Do chemical reactions occur around us all the time? (yes, no)

yes

Is it possible for some elements to have many different oxidation numbers? (yes, no)

yes

Is this reaction a redox reaction? (yes, no)

yes

Platinum and other rare metals are used in automobile catalytic convertors. Catalytic convertors change toxic automobile exhaust to less harmful products. For example, catalytic convertors react carbon monoxide with oxygen to form carbon dioxide. Are catalysts important for controlling pollution? (yes, no)

yes

Temperature has a significant effect on most reactions; first, because reaction rates usually increase with temperature, and second, because equilibrium constants change with temperature. For example, consider the equilibrium when CoCl2is dissolved in HCl (hydrochloric acid): The photograph above shows that at high temperature the blue form of cobalt is favored while at low temperature the pink form of cobalt is favored. Can temperature change the equilibrium position of a reaction? (yes, no)

yes

To be a redox reaction something must be oxidized and something must be reduced. Is this reaction a redox reaction? (yes, no)

yes