Chem unit 8. chemical reactions

If two compounds in a chemical reaction are listed with the coefficients 2 and 5 respectively, which is NOT a possible numerical combination of these compounds that will result in their complete reaction?

8 and 18 This is the only option that does not obey the explicit 2:5 ratio dictated by the coefficients in the chemical equation. All of the other values reduce to a 2:5 ratio.

Combination reactions, also known as synthesis reactions, are those that combine reactants to form a single compound having the general form

A + B ---> C

Mary conducts an experiment in which she pours a clear, colorless liquid into a beaker containing an aqueous solution. All of the properties below could indicate that a chemical change has occurred in her experiment EXCEPT which choice?

A cloudy white solid appeared suddenly in her solution. The cold beaker became very hot as soon as the liquids came into contact. The beaker began to smell like rotten eggs. The temperature of the beaker dropped slightly in response to an adjustment in the temperature of the lab.

Hydrogen peroxide, H2O2, can undergo spontaneous decomposition into water H2O and oxygen O2. Write the balanced chemical reaction with the simplest whole number coefficients.

A decomposition reaction means that a single reactant breaks down into multiple products. In this case, the two products are water and oxygen. The number of hydrogen and oxygen atoms on both sides of the equation must be balanced. The completed reaction is shown below. 2H2O2⟶2H2O+O2

For the following chemical equation: BaBr2(aq)+H2SO4(aq)→BaSO4(s)+2HBr(aq) which will NOT be involved in the net ionic equation?

Br−(aq) As the bromide ion is not involved in generating the precipitate, it will be a spectator ion, and therefore does not appear in the net ionic equation.

What is the coefficient for O2 in the balanced version of the following chemical equation: C2H4+O2→CO2+H2O

C2H4+3 O2→2 CO2+2 H2O 3

A familiar example of a weak acid is acetic acid, the main ingredient in food vinegars:

CH3CO2H(aq)+H2O(l)⇌CH3CO−2(aq)+H3O+(aq)

When carbon dioxide is dissolved in an aqueous solution of sodium hydroxide, the mixture reacts to yield aqueous sodium carbonate and liquid water. Determine the net ionic equation for this process.

CO2(aq)+2OH−(aq)⟶CO2−/3(aq)+H2O(l)

What is occurring in the following unbalanced reaction: ClO−3→ClO2

Chlorine is reduced. Oxygen is always assumed to have an oxidation number of −2, so it is neither oxidized nor reduced in the reaction. In ClO−3, the 3 oxygen atoms contribute a total of −6; with an overall molecular charge of −1, Cl must have an oxidation number of +5. In ClO2, the 2 oxygen atoms contribute a total of −4; with an overall neutral molecular charge, Cl must have an oxidation number of +4. Therefore, the chlorine atom goes from an oxidation number of +5 to +4, which means it has been reduced.

Some single displacement reactions involve one halogen replacing a less reactive halogen. Cl2, replaces iodine in NaI, producing I2 and NaCl. Write the balanced single displacement reaction below. Do not include the states of the reactants or products.

Cl_2 + 2Nai ----> i_2 + 2NaCl A single displacement reaction has the form AB+C→AC+B, where B and C swap places. For the given reactants, A is sodium, B is iodine, and C is chlorine. The number of each type of atom on both sides of the equation must be balanced. The completed reaction is shown below.

Identify which of the following is soluble in water. CsF BaSO4 Mg(OH)2 MnS

CsF Cesium fluoride is soluble according to the solubility rule that all compounds of group IA elements are soluble (Cs).

A neutralization reaction is a specific type of acid-base reaction in which the reactants are an acid and a base, producing a salt and water as products:

acid+base⟶salt+water To illustrate a neutralization reaction, consider what happens when a typical antacid such as milk of magnesia (an aqueous suspension of solid Mg(OH)2) is ingested to ease symptoms associated with excess stomach acid (HCl): Mg(OH)2(s)+2HCl(aq)⟶MgCl2(aq)+2H2O(l) Note that the products of this reaction are water and the salt magnesium chloride.

The chemical reactions described in which acids and bases dissolved in water produce hydronium and hydroxide ions, respectively, are (by definition

acid-base reactions. In these reactions, water serves as both a solvent and a reactant.

chemical change

always produces one or more types of matter that differ from the matter present before the change

If precipitation is not expected from a reaction, which of the following is indicated?

the products are soluble

oxidation-reduction reaction is

unambiguously defined as one in which the oxidation number of one or more species changes.

The nature of HCl is such that its reaction with water is essentially 100% efficient

virtually every HCl molecule that dissolves in water will undergo this reaction. Acids that completely react in this fashion are called strong acids

In all cases, these compounds react only partially and so are thus classified as

weak bases

Classify the following reactions as combination, decomposition, displacement, or double displacement reactions: a. 2H2(g)+O2(g)⟶2H2O(l) b. Zn(s)+Cu(NO3)2(aq)⟶Zn(NO3)2+Cu(s)

a. This reaction has two reactants and a single product, so it is a combination reaction. b. In this reaction, atoms of zinc replace atoms of copper in the compound with nitrate ions. There are two cations involved, Zn2+ and Cu2+, but only one anion, NO−3, which remains part of the compound in both the reactant and the product. Rather than forming a compound with a different anion, each cation has its corresponding neutral metal on the opposite side of the reaction arrow. This is a displacement reaction.

Which of the following reactions is stoichiometrically equivalent to the reaction shown below? Pb(OH)4+2H2SO4→Pb(SO4)2+4H2O

2Pb(OH)4+4H2SO4→2Pb(SO4)2+8H2O

Choose the coefficient for SiO2 in the balanced version of the following chemical equation, using only whole numbers: Si2H6+O2→SiO2+H2O

4 2Si_2H_6 + 7O_2 ---> 4SiO_2 + 6H_2O

Using the chemical equation provided, identify which of the following are the coefficients of the reactants. 4Fe+3O2⟶2Fe2O3

4 and 3

Steps in Balancing a Chemical Equation

1- Identify the most complex substance. 2- Beginning with that substance, choose an element(s) that appears in only one reactant and one product, if possible. Adjust the coefficients to obtain the same number of atoms of this element(s) on both sides. 3- Balance polyatomic ions (if present on both sides of the chemical equation) as a unit. 4- Balance the remaining atoms, usually ending with the least complex substance and using fractional coefficients if necessary. If a fractional coefficient has been used, multiply both sides of the equation by the denominator to obtain whole numbers for the coefficients. 5 - Count the numbers of atoms of each kind on both sides of the equation to be sure that the chemical equation is balanced.

guidelines are used to assign oxidation numbers:

1- The oxidation number of an atom in an elemental substance is zero. 2- The oxidation number of a monatomic ion is equal to the ion's charge. 3- Oxidation numbers for common nonmetals are usually assigned as follows: Hydrogen: +1 when combined with nonmetals; −1 when combined with metals Oxygen: −2 in most compounds; sometimes −1 (so-called peroxides); very rarely −12 (so-called superoxides); positive values when combined with F (values vary) Halogens: always −1 except when combined with oxygen or other halogens (positive oxidation numbers when combined with oxygen, varying values) 4- The sum of the oxidation numbers of all atoms in a molecule or polyatomic ion equals the charge on the molecule or ion.

Identify the balanced chemical equation.

2 O2+4 Fe→2 Fe2O3 C7H16+10 O2→7 CO2+8 H2O FeBr3+H2SO4→Fe2(SO4)3+HBr 2 Fe+3 Cl2→2 FeCl3 is correct

Aqueous potassium carbonate reacts with aqueous silver nitrate to precipitate silver carbonate. What is the net ionic equation.

2Ag+(aq)+CO2−3(aq)⟶Ag2CO3(s)

the combustion of octane is described by the reaction below:

2C8H18(l)+25O2(g)⟶16CO2(g)+18H2O(g).

Aqueous potassium carbonate reacts with aqueous silver nitrate to precipitate silver carbonate. What is the complete ionic equation of this reaction?

2K+(aq)+CO2−3(aq)+2Ag+(aq)+2NO−3(aq) ⟶2K+(aq)+2NO−3(aq)+Ag2CO3(s)

Determine a balanced equation for the reaction of molecular nitrogen (N2) and oxygen (O2) to form dinitrogen pentoxide

2N2+5O2→2N2O5

Which of the following is NOT water-soluble? NaCl K2SO4 AgCl NH3

AgCl According to the solubility rules, all chloride (Cl−), bromide (Br−), and iodide (I−) salts are water soluble, except for those of Ag+, Pb2+, and Hg2+2.

silver chloride

AgNO3(aq)+NaCl(aq)⟶NaNO3(aq)+AgCl(s).

Which of the following compounds would form a precipitate in solution? LiNO3 AlPO4 CsBr RbHCO3

AlPO4 Phosphates are typically insoluble, and aluminum is not an exception to this rule.

chemical property

Examples of chemical properties include flammability, toxicity, acidity, reactivity, and heat of combustion.

Identify the missing product in the following acid-base reaction. Fe(OH)_2 + 2HF ---> _____ + 2H_2O

FeF_2

What is the coefficient for Fe(s) in the balanced version of the following chemical equation: ___?Fe(s)+___O2(g)→___Fe2O3(s)

First, write the unbalanced equation: Fe(s)+O2(g)→Fe2O3(s) To balance O2(g), add 3 in front of O2(g) and add 2 in front of Fe2O3(s): Fe(s)+3O2(g)→2Fe2O3(s) To balance Fe(s), add 4 in front of Fe(s): 4Fe(s)+3O2(g)→2Fe2O3(s) The equation is balanced. The coefficient for Fe(s) is 4.

What gaseous product is liberated in gas evolution reactions involving sulfides?

H2S(g)

Which of the following dissolves in water to yield hydronium ions? Select all that apply.

HBr, HNO3, and HI are strong acids: each of these will donate an acidic proton to water to generate hydronium in solution. NaCl will also dissolve in water but has no acidic protons, and thus will produce no hydronium ions in solution.

Predict the products of the following acid-base reaction. Do not write any coefficients equal to 1 HCl (aq) + NaOH (aq) ---> ____ (L) + ____ (aq)

HCl (aq) + NaOH (aq) ---> H_2O (L) + NaCl (aq)

In which compound does oxygen have an oxidation number other than −2?

H_2O_2 In peroxides like hydrogen peroxide, oxygen has an oxidation number of -1, due to the fact that the two oxygen atoms are covalently bound to one another.

Diatomic Elements

Hydrogen Nitrogen (N2) Oxygen Fluorine Chlorine Bromine Iodine

Magnesium, Mg, will undergo a single displacement reaction with hydrogen chloride (a strong acid, HCl). The products are hydrogen gas, H2, and magnesium chloride, MgCl2. Write the balanced single displacement reaction below.

Mg+2HCl ---> MgCl_2+H_2

When ammonium is found in solution, which gas might we anticipate being produced?

NH3 Ammonium salts have the potential to produce ammonia gas

Fill in the blanks with the reactant and products in the balanced equation for the gas evolution reaction of ammonium bromide, NH4Br, with sodium hydroxide. The reaction produces water and two other products. Do NOT include the designations for the states of matter in your answer.

NH4Br+NaOH⟶NH3+H2O+NaBr The sodium and the bromine in the reactants are missing in the products, as well as two hydrogens and an oxygen. They must be added. The OH from the sodium hydroxide plus the extra hydrogen on the ammonium ion can combine to form a water molecule, and the sodium and bromine can combine to form sodium bromide. The complete reaction is shown below

For the following chemical equation: Zn(NO3)2(aq)+H2S(aq)→ZnS(s)+2HNO3(aq) Which will NOT be involved in the net ionic equation? NO−3 (aq) Zn2+ (aq) S2− (aq) ZnS (s)

NO−3 (aq) As the nitrate ion is not involved in generating the precipitate, it will be a spectator ion, and therefore does not appear in the net ionic equation.

Fill in the blanks with reactants and products in the balanced equation for the acidification reaction of sodium sulfide by hydrobromic acid. Note the phases for each compound are provided.

Na2S(aq)+2HBr(aq)⟶H2S(g)+2NaBr(aq)

Sodium bisulfite, NaHSO3, reacts with hydrochloric acid in a gas evolution reaction, producing water and two other products. Write the chemical formulas for the other two products to complete the reaction in molecular form

NaHSO3(aq)+HCl(aq)⟶SO2(g)+H2O(l)+NaCl(aq)

chemical change examples

One of the chemical properties of iron is that it rusts - one of the chemical properties of chromium is that it does not. -The explosion of nitroglycerin --Other examples of chemical changes include controlled reactions performed in a lab (such as copper reacting with nitric acid), all forms of combustion (burning), and food being cooked, digested, or rotting

physical changes

Phase changes or simple mixing of substances are example of (ex) Mixing ethanol and water is another example of a physical process

Given C+2H2SO4→CO2+2SO2+2H2O, identify which element is reduced.

S

2Li+S→Li2S is a redox reaction. Identify which of the following is the oxidizing agent and its change in oxidation number.

S is the oxidizing agent, oxidation change from 0 to 2−

Identify the missing product in the following acid-base reaction. Include the coefficient only if it is larger than 1 in the balanced equation.

Since one of the reactants is H2CO3, the carbonate ion must be CO2−3. The lithium ion is Li+, therefore, an ionic compound with lithium and the carbonate ion has the formula Li2CO3. Filling this compound in our equation, we can now see that it is balanced. Notice that there are 2OH− ions on the left side (since there are 2LiOH molecules) and 2H+ ions from H2CO3. These combine to form 2HOH or H2O molecules, as indicated. The balanced equation is shown below. H2CO3+2LiOH⟶Li2CO3+2H2O

What occurs in a precipitation reaction?

Soluble substances combine to form a solid that is insoluble in the reaction solution. A precipitation reaction occurs when two solvated (usually aqueous) ions combine to form a solid precipitate.

Identify if the equation below represents a redox reaction and if appropriate, name the oxidant and the reductant: C2H4(g)+3O2(g)⟶2CO2(g)+2H2O(l)

This is a redox reaction. The reducing agent is ethylene, C2H4. The oxidizing agent is oxygen, O2. This is a redox reaction (combustion). Carbon is oxidized, its oxidation number increasing from −2 in C2H4 to +4 in CO2. The reducing agent is C2H4. Oxygen is reduced, its oxidation number decreasing from 0 in O2 to −2 in H2O. The oxidizing agent is O2.

In what type of reaction do bonds only break and not form?

With a decomposition reaction, one substance breaks into two, so bonds will only break and not form. An example reaction is

Digestion of proteins in the stomach is an example of what?

a chemical change

If two substances are mixed together and as a result a new color is produced, this is evidence of which of the following?

a chemical change

The following equation is an example of which of the following? CH4(g)+2O2(g)⟶CO2(g)+2H2O(g)

a chemical change (combustion reaction) This is an example of a combustion reaction. The hallmark of such a reaction is the presence of oxygen gas as a reactant and the formation of carbon dioxide and water.

The equation below is an example of which of the following? AgNO3(aq)+NaCl(aq)⟶NaNO3(aq)+AgCl(s)

a chemical change (precipitation reaction) This is an example of a precipitation chemical reaction. Notice that the product silver chloride is marked as a solid. Since it is not soluble in water, it precipitates

An acid-base reaction is one in which

a hydrogen cation (H+, which is actually just a proton) is transferred from one chemical species to another. Such reactions are of central importance to numerous natural and technological processes, ranging from chemical transformations within cells and lakes and oceans, to the industrial-scale production of fertilizers, pharmaceuticals, and other substances essential to society.

chemical change more examples

abrupt change in temperature (cold to hot OR hot to cold), a change in the color of the substance, an odor, formation of a precipitate, and a release of gas to form bubbles. A chemical change may be accompanied by any number of these physical indications.

The subscripts

are part of the formulas and once the formulas for the reactants and products are determined, the subscripts may not be changed

Single-displacement (replacement) reactions

are redox reactions in which an ion in solution is displaced (or replaced) via the oxidation of a metallic element

If we expect a precipitate to be formed in a certain reaction that takes place in solution, this implies that:

at least one of the products is insoluble

single displacement

bonds are both broken and formed. 2 things become 1

In a chemical equation, the number of molecules (or formula units) of a particular substance that are participating in the chemical reaction is indicated by a:

coefficient

The equation that contains spectator ions is called the:

complete ionic equation The complete ionic equation contains all the ions in solution, including spectator ions.

What is the type of reaction involved in the following equation? Al(s)+Fe2O3(s)⟶2Fe(s)+Al2O3(s)

displacement reaction

Acid-base gas evolution reactions come under which type of reactions?

double displacement reaction Acid-base gas evolution reactions involve a double displacement reaction that forms water and an unstable molecule that then decomposes into a gas and a stable compound.

Which of the following can be characterized as a chemical change? food digestion by a human the condensation of water the evaporation of ethanol the combustion of ethanol

food digestion by human combustion of ethanol

The substances that are present at the beginning are called reactants and the substances present at the end are called products.

in a chemical change

The coefficients

indicate the number of each substance involved in the reaction and may be changed in order to balance the equation

A base is a substance that will dissolve in water to yield hydroxide ions (OH−). The most common bases are

ionic compounds composed of alkali or alkaline earth metal cations (groups 1 and 2) and the hydroxide ion

In the equation 5Z→2A+3B, how many molecules of Z must react to give 15 molecules of B?

multply whole equation by 5 to get 15B. 5 (5Z --> 2A + 3B) = 25Z --> 10A + 15B =25 molecules of Z

The oxidation number (or oxidation state) an

on is just the charge of the ion. The oxidation number of an atom in a molecule is the charge that atom would possess if the molecule was ionic.

A base is something that:

produces an OH− ion when dissolved in water. A base is a substance that will dissolve in water to yield hydroxide ions (OH−).

The substances generated by the chemical reaction are known as:

products

oxidation = increase in oxidation number

reduction = decrease in oxidation number

Weak acids, such as those

responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor, are commonly encountered in nature.

In a chemical equation, the number of atoms of a particular element that are present in a substance is indicated by a:

subscript