Chapter 6: Energy Changes, Reaction Rates, and Equilibrium
Which value (if any) in each pair corresponds to a slower reaction
Ea = 100 kcal
For a system at chemical equilibrium,
A) forward and reverse reaction rates are equal.
Which of the following will increase the rate of a reaction?
All of these changes will increase the rate of a reaction.
The ΔH for the reaction depicted by the energy diagram below is ________.
Answer: -25 kJ
Which term correctly describes a reaction in which the energy of the products is higher than the energy of the reactants?
Endothermic
Which bond is the strongest (shortest bond)?
H-F
Which bond is the weakest (longest bond)?
H-I
Which of the following statements about activation energy is correct?
It is low for reactions that take place rapidly.
Breaking a chemical bond requires energy.
TRUE
The rusting of iron is described by the reaction: 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s). The formation of rust on an exposed piece of iron typically takes several months. Which of the following is NOT a reasonable assumption about this chemical reaction?
The formation of rust has a low activation energy.
The rate of a chemical reaction increases with an increase in the concentration of one or more reactants. This is best explained by which statement?
The higher concentration of reactants increases the frequency of collisions between molecules.
The minimum combined kinetic energy reactant particles must possess in order for their collision to result in a reaction is called the
activation energy.
Increasing the temperature at which a chemical reaction occurs
cause more reactant collisions to take place in a given time
Which of the following energy quantities is equivalent to 578 J? (4.184 x 103 J = 1 kcal)
0.138 kcal
Consider the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = -531 kcal/mol. How much heat is released when 3.40 × 1020 molecules of C3H8(g) is burned?
0.300 kcal
Which quantity represents the largest amount of stored energy?
10 grams of fat
Which of the following energy quantities is equivalent to 258 Cal?
1080 kJ
Consider the combustion reaction of propane: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = -531 kcal. If 6.70 × 104 kcal of energy is released in the reaction, how many grams of oxygen were consumed?
2.02 × 104 g of O2
A peanut butter and jelly sandwich contain 9.00 g of fat, 6.00 g of protein, and 25.0 g of carbohydrate. (Protein and carbohydrates both contain 4 calories per gram, while fat provides 9 calories per gram) How many Calories does this sandwich provide?
205 Cal
.A chemical reaction releases 55.2 kcal. How many kilojoules does this correspond to? (4.184 kJ = 1 kcal)
231 kJ
Consider the combustion reaction of propane: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = -531 kcal. If 1.24 × 105 kcal of energy is released in the reaction, how many moles of propane were burned?
234 mol of C3H8
Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where ΔH = -137 kJ. How many kilojoules are released when 55.3 g of C2H4 reacts?
270. kJ are released
Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where ΔH = -137 kJ. How many kilojoules are released when 3.5 mol of C2H4 reacts?
480 kJ are released
Which of the following energy quantities is equivalent to 11.9 kcal?
49.8 kJ
Which of the following is the correct equilibrium constant expression for the reaction
4HCI(g) + O2(g) --> <-- 2H2O(g) + 2CI2(g)
A chemical reaction requires 31.39 kJ. How many kilocalories does this correspond to?
7.502 kcal
Consider the reaction, 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g), where ΔH = -137 kJ. How many kilojoules are released when 92.3 g of NO2 reacts?
91.6 kJ are released
Which of the following is ALWAYS necessary for a chemical reaction to occur between two reactants, A and B?
A and B must collide with the proper orientation and with a certain minimum amount of energy.
Which statement about catalysts is NOT true?
A catalyst lowers the ΔH of a chemical reaction.
Which of the following is a true statement about the energy diagram shown below?
A labels the Ea of the reaction and B labels ΔH of the reaction.
A manufacturing company requires 157 kJ of energy to power one of its machines for a day. The reaction shown below would be able to provide a sufficient amount of energy for this purpose. 2 HgO(s) → 2 Hg(l) + O2(g) ΔH = 182 kJ
Answer: FALSE
An endothermic reaction is one in which energy is absorbed and ΔH is negative (-).
Answer: FALSE
Catalysts increase reaction rate by providing an alternate reaction pathway with a higher activation energy.
Answer: FALSE
Chemical reactions are considered favorable if the products have a higher energy than the reactants.
Answer: FALSE
Consider the reaction: 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g). Increasing the concentration of C2H6(g) will decrease the activation energy.
Answer: FALSE
In the energy diagram shown below, the ΔH of the reaction is labeled by D.
Answer: FALSE
Increasing the concentration of reactants makes collisions between the reactant and other reactants less likely because of "more crowded conditions."
Answer: FALSE
Increasing the temperature of a reaction mixture usually results in a decrease in the reaction rate.
Answer: FALSE
Reactions with high Ea are generally fast reactions.
Answer: FALSE
16. Exothermic reactions involve the formation of products having lower energy than the reactants.
Answer: TRUE
18. Changes in potential energy occur in chemical reactions.
Answer: TRUE
Activation energy is the minimum amount of energy necessary for a reaction to occur.
Answer: TRUE
Ammonia (NH3) is synthesized by the reaction of nitrogen and hydrogen in the presence of an iron catalyst according to the equation below. Removing the iron catalyst would decrease the reaction rate.
Answer: TRUE
Bond breaking is endothermic.
Answer: TRUE
Bond dissociation energies are always positive numbers.
Answer: TRUE
Consider the reaction: 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g). Decreasing the concentration of C2H6(g) will decrease the reaction rate.
Answer: TRUE
Enzymes are proteins that act as biological catalysts.
Answer: TRUE
In a slow reaction, the activation energy is far greater than the average energy content of the reacting particles.
Answer: TRUE
Increasing the concentration of the reactants in a chemical reaction increases the number of collisions, and the reaction rate increases.
Answer: TRUE
Kinetic energy is the energy associated with movement; potential energy is the energy inherent in an object due to its position or composition.
Answer: TRUE
Orientation relative to one another, at the moment of collision, is always a factor in determining whether a collision is effective.
Answer: TRUE
The collision between two reactant molecules does not always result in the formation of reaction products.
Answer: TRUE
The difference in energy between the reactants and the transition state is called the energy of activation, symbolized by Ea.
Answer: TRUE
The energy of the reacting molecules affects whether a particular collision will lead to a chemical reaction.
Answer: TRUE
The stronger the bond, the higher its bond dissociation energy.
Answer: TRUE
When reactants are in the solid state, reaction rate increases as temperature increases and decreases as state of subdivision (particle size) increases.
Answer: TRUE
An enzyme contains a region called its ________ that binds a reactant, which then undergoes a very specific reaction with an enhanced rate.
Answer: active site
As a general rule, a reaction rate ________ for each 10 °C the temperature is raised.
Answer: doubles
Heat is absorbed in an ________ reaction.
Answer: endothermic
Biological catalysts held together in a very specific three-dimensional shape are called ________.
Answer: enzymes
In an ________ reaction, the products are lower in energy than the reactants.
Answer: exothermic
The enzyme lactose aids in the digestion of ________. Answer: lactose
Answer: lactose
When ΔH is negative, the bonds formed in the products are ________ than the bonds broken in the reactants.
Answer: stronger
In the energy diagram shown below, C labels the ________.
Answer: transition state
In writing an equilibrium constant expression, which of the following is incorrect?
Concentrations of pure solids and pure liquids are always placed in the denominator of the expression.
Which value (if any) in each pair corresponds to a faster reaction?
Ea = 1 kcal
Energy is the capacity to do work.
TRUE
Which of the following is NOT a reasonable assumption about the chemical reaction whose energy diagram is depicted below?
The activation energy for the reaction is 100kJ.
Consider the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = -531 kcal. Which statement concerning this reaction is true?
The bonds formed in the products are stronger than the bonds broken in the reactants.
The law of conservation of energy states that ________.
energy cannot be neither created nor destroyed
For a collision between molecules to result in reaction, the molecules must possess a certain minimum energy and
have a favorable orientation relative to each other when they collide.
Whether a reaction is exothermic or endothermic is determined by
how reactant and product potential energies compare.
In the reaction: 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g), increasing the concentration of C2H6(g) will ________.
increase the reaction rate
36. Most reactions are carried out in liquid solution or in the gaseous phase because in such situations
it is easier for reactants to come in contact with each other.
Catalysts accelerate a reaction by ________.
lowering the energy of activation
Chemical equilibrium is reached in a system when
reactants are being consumed at the same rate they are being produced
Which of the following changes will decrease reaction rate for the chemical reaction 2CO + O2 → 2CO2
removing some CO from the reaction mixture
Catalysts are correctly characterized by each of the following statements except one. The exception is
they do not actively participate in a reaction.
