Chpater 7 Review
Completion
Complete each sentence or statement.
1. The statement that in chemical reactions, the total mass of the reactants equals the total mass of the products
is the law of _________________________.
2. In an experiment, 44 g of propane was burned, producing 132 g of carbon dioxide and
mass of oxygen that was needed for the reaction was ____________________.
of water. The
3. A(An) ____________________ is the number that appears before a formula in a chemical equation.
4. The molar mass of carbon is ____________________.
5. A sample of NaCl contains 188 g of the compound. The sample contains ____________________ moles of
NaCl.
6. Butane burns as shown in the balanced chemical equation 2C4H10 + 13O2  10H2O + 8CO2. If 6 mol of
butane burn, ____________________ mol of carbon dioxide are produced.
7. An iron fence is left unpainted, and it reacts with the oxygen in the air, forming rust. The formation of rust is
an oxidation-reduction reaction, but it is also an example of a(an) ____________________ reaction.
8. Single-replacement reactions can take place with nonmetals. In the following equation, assume that A and C
are nonmetals and B is a metal. Complete the following general equation for the replacement of a nonmetal in
a compound by another nonmetal: A + BC  ____________________.
9. The element ____________________ is always present in a combustion reaction.
10. In a double-replacement reaction, there are two reactants and ____________________ product(s).
11. When fluorine reacts with a metal, it forms an F– ion. The fluorine atom has gained an electron and undergone
____________________.
12. During a chemical reaction, energy is released during the ____________________ of chemical bonds.
13. In terms of energy, the general chemical equation AB + CD + energy  AD + CB represents a(an)
____________________ reaction.
14. Cooking requires continuous addition of energy to the chemical reactions that are taking place. The chemical
reactions involved in cooking can be described as ____________________.
15. For a certain chemical reaction, the reactants contain 385 kJ of chemical energy, and the products contain 366
kJ of chemical energy. In order for energy to be conserved, 19 kJ of energy must be ____________________.
16. Measuring how quickly a reactant disappears is one way to measure the ____________________ of the
reaction.
17. A chunk of limestone, which is calcium carbonate, reacts with acid at a certain rate. If the limestone were
crushed, the rate of reaction between the acid and the limestone would ____________________.
18. A catalyst is used in a catalytic converter in vehicles to help control pollution. For example, the catalytic
converter ____________________ the rate at which carbon monoxide is oxidized to carbon dioxide. (2CO +
O2 2CO2)
19. The statement that when a change is introduced to a system in equilibrium, the equilibrium shifts in the
direction that relieves the stress on the system is known as _________________________.
20. Many manufacturing processes involve chemical reactions that reach equilibrium. One way to increase the
amount of product formed is to decrease the ____________________ of the product in the system.
Short Answer
21. How does the law of conservation of mass explain why only a bit of ash is left after burning a large sheet of
paper?
22. What is the purpose of balancing a chemical equation?
23. A student balanced the chemical equation Mg + O2  MgO by writing Mg + O2  MgO2. Was the equation
balanced correctly? Explain your answer. If the equation was not balanced correctly, write the correctly
balanced equation.
24. How many moles of nitrogen are contained in 4.20  1024 atoms of nitrogen?
25. How many grams of O2 are in 5.0 mol of the element?
26. In a decomposition reaction, a compound is broken down into two or more simpler substances. Explain why
the term compound is used to refer to the reactant and the term substances is used to refer to the products.
27. Magnesium will replace silver in a compound. What are the products of a single-replacement reaction
between magnesium and silver nitrate?
28. What are the products of the double-replacement reaction between potassium chloride and silver acetate?
29. When most fuels burn, water and carbon dioxide are the two main products. Why can’t you say that water and
carbon dioxide are products of all combustion reactions?
30. In the reaction between bromine and sodium, a bromine atom gains an electron. What ion is formed? Is the
bromine oxidized, or is it reduced?
31. Contrast the forming and breaking of chemical bonds in terms of energy changes.
32. Explain how energy is conserved during chemical reactions.
33. Explain why batteries and film will stay fresh longer if they are kept in a refrigerator or freezer.
34. Explain why ice in liquid water at 0ºC is an example of physical equilibrium.
Figure 7-1
35. In Figure 7-1, both the reactants and the product of the reaction are gases. In this equilibrium, the reaction that
produces fewer gas molecules is favored. Explain why increasing the pressure on the reaction favors the
formation of ammonia rather than the formation of the reactants.
Problem
36. Balance the following chemical equation.
Cu + HNO3  Cu(NO3)2 + NO2 + H2O
37. When iron metal reacts with oxygen, the reaction can form Fe2O3. Write a balanced chemical equation for this
reaction, and find the number of moles of oxygen that are needed to form 6 mol of Fe2O3.
38. Sodium reacts with chlorine gas to form sodium chloride. Write a balanced chemical equation for the
reaction, and find the mass of chlorine gas that will react with 96.6 g of sodium.
Essay
39. Which two types of reactions are also always redox reactions? Explain your answer.
40. Explain the difference between a physical equilibrium and a chemical equilibrium.
Chpater 7 Review
Answer Section
COMPLETION
1. ANS: conservation of mass
DIF: L1
2. ANS: 160 g
OBJ: 7.1.1
STO: D.12.4, D.12.10
DIF: L2
3. ANS: coefficient
OBJ: 7.1.1
STO: D.12.4, D.12.10
DIF: L1
4. ANS: 12.0 g/mol
OBJ: 7.1.2
DIF: L1
5. ANS: 3.2
OBJ: 7.1.3
DIF: L2
6. ANS: 24
OBJ: 7.1.3
DIF: L1
7. ANS: synthesis
OBJ: 7.1.4
DIF: L2
8. ANS: C + BA
OBJ: 7.2.1
STO: D.12.4
DIF: L2
9. ANS: oxygen
OBJ: 7.2.1
STO: D.12.4
DIF: L1
10. ANS: two
OBJ: 7.2.1
STO: D.12.4
DIF: L1
11. ANS: reduction
OBJ: 7.2.1
STO: D.12.4
DIF: L1
12. ANS: formation
OBJ: 7.2.2
STO: D.12.6
DIF: L2
13. ANS: endothermic
OBJ: 7.3.1
STO: D.12.3
DIF: L1
14. ANS: endothermic
OBJ: 7.3.2
STO: D.12.6
DIF: L2
15. ANS: released
OBJ: 7.3.2
STO: D.12.6
DIF: L2
16. ANS: rate
OBJ: 7.3.3
DIF: L1
17. ANS: increase
OBJ: 7.4.1
DIF: L2
18. ANS: speeds up
OBJ: 7.4.1
STO: D.12.10
DIF: L2
OBJ: 7.4.1
19. ANS: Le Châtelier’s principle
DIF: L1
OBJ: 7.5.2
20. ANS: concentration
DIF: L2
OBJ: 7.5.2
SHORT ANSWER
21. ANS:
In addition to the ash, gases are formed. The total mass of the paper and oxygen equals the total mass of the
ash and the gases formed.
DIF: L1
OBJ: 7.1.1
STO: D.12.4, D.12.10
22. ANS:
A balanced chemical equation shows that mass is conserved. The number of each type of atom in the reactants
must equal the number of each type of atom in the products.
DIF: L1
OBJ: 7.1.2
23. ANS:
The equation was not balanced correctly because it was balanced by changing a subscript instead of changing
coefficients. The correctly balanced equation is 2Mg + O2  2MgO.
DIF: L2
24. ANS:
6.98 mol
OBJ: 7.1.2
DIF: L2
OBJ: 7.1.3
25. ANS:
The molar mass of O2 is 16 g/mol, so 5.0 mol of O2 have a mass of 80 g.
DIF: L1
OBJ: 7.1.3
26. ANS:
The reactant must be a compound because it is being broken down; an element cannot be broken down in a
chemical reaction. The products can be either compounds or elements, and substances include both
compounds and elements.
DIF: L2
OBJ: 7.2.1
STO: D.12.4
27. ANS:
magnesium nitrate, Mg(NO3)2, and silver, Ag
DIF: L1
OBJ: 7.2.1
28. ANS:
silver chloride and potassium acetate
STO: D.12.4
DIF: L1
OBJ: 7.2.1
STO: D.12.4
29. ANS:
Some other substances, such as hydrogen, also burn. When the fuel does not contain carbon, carbon dioxide
does not form.
DIF: L2
OBJ: 7.2.1
STO: D.12.4
30. ANS:
The bromide ion, Br–, forms. The bromine is reduced.
DIF: L1
OBJ: 7.2.2
STO: D.12.6
31. ANS:
Forming chemical bonds releases energy. Breaking chemical bonds requires (absorbs) energy.
DIF: L1
OBJ: 7.3.1
STO: D.12.3
32. ANS:
The amount of energy contained in the bonds of the reactants plus any energy absorbed by the reactants to
break the bonds must equal the amount of energy contained in the bonds of the products plus any energy
given off when the products are formed.
DIF: L1
OBJ: 7.3.3
STO: D.12.10
33. ANS:
Lowering the temperature lowers the rate of reaction, so the reactants in the film and batteries are less likely
to react before they are used.
DIF: L2
OBJ: 7.4.1
34. ANS:
Equilibrium exists because liquid water is freezing and ice is melting at the same rate. The equilibrium is
physical because no new substances form.
DIF: L1
OBJ: 7.5.1
35. ANS:
There are more gas molecules on the reactant side. Increased pressure will thus cause the system to shift in the
direction that decreases the pressure of the system (that is, produces fewer gas molecules) and the reaction
will shift to form more product.
DIF: L1
OBJ: 7.5.2
PROBLEM
36. ANS:
Cu + 4HNO3  Cu(NO3)2 + 2NO2 + 2H2O
DIF: L2
OBJ: 7.1.2
37. ANS:
4Fe + 3O2  2Fe2O3; 9 mol O2
DIF: L2
OBJ: 7.1.4
38. ANS:
2Na + Cl2  2NaCl; 149 g Cl2
DIF: L2
OBJ: 7.1.4
ESSAY
39. ANS:
Single-replacement reactions are redox reactions because one element in the compound is reduced, and the
free element is oxidized. Combustion is a redox reaction because oxygen is always reduced, and another
element is oxidized.
DIF: L2
OBJ: 7.2.2
STO: D.12.6
40. ANS:
In a physical equilibrium, there is a difference in the form of the substance, but its chemical composition
remains the same. In a chemical equilibrium, chemical changes occur, and the reactants are different
substances than the products.
DIF: L2
OBJ: 7.5.1