ACS CHEMISTRY FINAL PRACTICE
CONCEPTUAL QUESTIONS &
ANSWERS
SQ-6: Carbonated beverages have a fizz because of gas dissolved in the solution. What
increases the concentration of gas in a solution?
Solutions and Aqueous Reactions, Part 2
a) cooling the solution
b) heating the solution
c) increasing the volume of solution
d) decreasing the volume of the solution - Correct Answers -a) cooling the solution
Explanation:
Using Henry's Law (is a constant for a gas at a given temperature and as temperature
increases, solubility of a gas decreases or k decreases)
As the pressure of the gas increases, the concentration of the gas increases.
Volume of the solution will not change the concentration of the gas
PQ-4: Which Substance is most soluble in water?
Solutions and Aqueous Reactions, Part 2
a) ethane, CH3CH3
b) ethanol, CH3CH2OH
c) n-butane, CH3CH2CH2CH3
d) 1-butanol, CH3CH2CH2CH2OH - Correct Answers -b) ethanol, CH3CH2OH
PQ-11: The solubility of a substance is 60g per 100mL of water at 15C. A solution of
this substance is prepared by dissolving 75 g in 100mL of water at 75C. The solution is
then cooled slowly to 15C without any solid separating. The solution is
Solutions and Aqueous Reactions, Part 2
a) supersaturated at 75C
b) supersaturated at 15C
c) unsaturated at 15C
d) saturated at 15C - Correct Answers -b) supersaturated at 15C
PQ-14: How will you increase the solubility of oxygen in water? The partial pressure of
oxygen (PO2) is 0.21 atm in air at 1 atm (Pext)
Solutions and Aqueous Reactions, Part 2
,a) increase PO2, but keep Pext constant
b) decrease PO2, but keep Pext constant
c) increase Pext but keep Po2 constant
d) decrease Pext but keep Po2 constant - Correct Answers -a) increase PO2, but keep
Pext constant
PQ-19: Consider pure water separated from an aqueous sugar solution by a
semipermeable membrane. After some time has passed, what (if anything) will happen
to the concentration of the sugar solution?
Solutions and Aqueous Reactions, Part 2
a) it will decrease
b) it will increase
c) it will remain the same
d) it cannot be determined - Correct Answers -a) it will decrease
SQ-2: The rate law for the reaction
A + B --> C + D
is first order in [A] and second order in [B]. If [A] is halved and [B] is doubled, the rate of
the reaction will.
Kinetics
a) remain the same
b) be increased by a factor of 2
c) be increased by a factor of 4
d) be increased by a factor of 8 - Correct Answers -b) be increased by a factor of 2
Explanation:
order of the reaction with respect to each reactant
[A] is 1 and [B] is 2
Since it is [A] 1/2 and [B] 4 it is 2
SQ-7: Which statement regarding chemical reactions is true according to collision
theory?
Kinetics
a) all molecular collisions result in chemical reactions
b) catalysts make individual collisions more effective, increasing reaction rates
c) Proper orientation of molecules is required for collision to result in chemical reactions
d) Increasing the temperature of a reaction decrease the kinetic energy of molecules,
making collisions more effective - Correct Answers -c) Proper orientation of molecules is
required for collision to result in chemical reactions
Explanation:
, You know that for a collision to lead to a chemical reaction it must satisfy two criteria.
The collision must have sufficient energy for the reaction to occur. Also, the molecules
must be in the proper orientation for the collision to be effective. Therefore, not all
collisions result in a chemical reaction. Therefore choice (A) is incorrect.
The presence of a catalyst does increase the rate of a reaction. However, the way a
catalyst increases the rate of a reaction is not by making the collisions more effective.
Instead a catalyst increases the rate of a reaction by providing an alternative route from
reactants to products that has a smaller activation energy. Processes with smaller
activation energies result in a faster reaction rate. Therefore choice (B) is incorrect
Increasing the temperature often leads to an increase in the rate ofa reaction. However,
the reason is because as the temperature increases the average kinetic energy ofthe
reactants increases. This can increase the rate of a reaction in two ways. First, there
are more collisions that have the minimum energy needed for a reaction to occur.
Second, the higher kinetic energy increases the number of collisions, which means the
odds of a collision having the proper orientation increases. This increases the rate of a
reaction. Therefore choice (D) is incorrect.
Consider this equilibrium:
2SO2(g) +O2(g) --> 2SO3(g)
The forward reaction is proceeding at a certain rate at some temperature and pressure.
When the pressure is increased, what might we expect for the forward reaction?
Kinetics
a) a greater rate of reaction and a greater yield of SO3 at equilibrium
b) a greater rate of reaction and a same yield of SO3 at equilibrium
c) a lesser rate of reaction and a smaller yielf of SO3 at equlibrium
d) a lesser rate of reaction and a greater yield of S03 at equilibrium - Correct Answers -
a) a greater rate of reaction and a greater yield of SO3 at equilibrium
Explanation:
Le Chatlier's Principle
You know that a change in pressure may shift the equilibrium and depends on the
moles of gaseous substances as reactants and products. An increase in pressure will
shift the equilibrium in the direction that minimizes the increase in pressure. This is the
side that has the fewest moles of gas. For this reaction, the side with fewer moles of gas
is the product side. You realize that this means that an increase in pressure will cause
the rate of the reaction producing S03 to increase.
PQ-4: The gas phase reaction A2 + B2 --> 2AB, proceeds by bimolecular collisions
between A2 and B2 molecules. The rate law is rate=k[A2][B2]
If the concentrations of both A2 and B2 are doubled, the reaction rate will change by a
factor of
Kinetics
a) 1/2
CONCEPTUAL QUESTIONS &
ANSWERS
SQ-6: Carbonated beverages have a fizz because of gas dissolved in the solution. What
increases the concentration of gas in a solution?
Solutions and Aqueous Reactions, Part 2
a) cooling the solution
b) heating the solution
c) increasing the volume of solution
d) decreasing the volume of the solution - Correct Answers -a) cooling the solution
Explanation:
Using Henry's Law (is a constant for a gas at a given temperature and as temperature
increases, solubility of a gas decreases or k decreases)
As the pressure of the gas increases, the concentration of the gas increases.
Volume of the solution will not change the concentration of the gas
PQ-4: Which Substance is most soluble in water?
Solutions and Aqueous Reactions, Part 2
a) ethane, CH3CH3
b) ethanol, CH3CH2OH
c) n-butane, CH3CH2CH2CH3
d) 1-butanol, CH3CH2CH2CH2OH - Correct Answers -b) ethanol, CH3CH2OH
PQ-11: The solubility of a substance is 60g per 100mL of water at 15C. A solution of
this substance is prepared by dissolving 75 g in 100mL of water at 75C. The solution is
then cooled slowly to 15C without any solid separating. The solution is
Solutions and Aqueous Reactions, Part 2
a) supersaturated at 75C
b) supersaturated at 15C
c) unsaturated at 15C
d) saturated at 15C - Correct Answers -b) supersaturated at 15C
PQ-14: How will you increase the solubility of oxygen in water? The partial pressure of
oxygen (PO2) is 0.21 atm in air at 1 atm (Pext)
Solutions and Aqueous Reactions, Part 2
,a) increase PO2, but keep Pext constant
b) decrease PO2, but keep Pext constant
c) increase Pext but keep Po2 constant
d) decrease Pext but keep Po2 constant - Correct Answers -a) increase PO2, but keep
Pext constant
PQ-19: Consider pure water separated from an aqueous sugar solution by a
semipermeable membrane. After some time has passed, what (if anything) will happen
to the concentration of the sugar solution?
Solutions and Aqueous Reactions, Part 2
a) it will decrease
b) it will increase
c) it will remain the same
d) it cannot be determined - Correct Answers -a) it will decrease
SQ-2: The rate law for the reaction
A + B --> C + D
is first order in [A] and second order in [B]. If [A] is halved and [B] is doubled, the rate of
the reaction will.
Kinetics
a) remain the same
b) be increased by a factor of 2
c) be increased by a factor of 4
d) be increased by a factor of 8 - Correct Answers -b) be increased by a factor of 2
Explanation:
order of the reaction with respect to each reactant
[A] is 1 and [B] is 2
Since it is [A] 1/2 and [B] 4 it is 2
SQ-7: Which statement regarding chemical reactions is true according to collision
theory?
Kinetics
a) all molecular collisions result in chemical reactions
b) catalysts make individual collisions more effective, increasing reaction rates
c) Proper orientation of molecules is required for collision to result in chemical reactions
d) Increasing the temperature of a reaction decrease the kinetic energy of molecules,
making collisions more effective - Correct Answers -c) Proper orientation of molecules is
required for collision to result in chemical reactions
Explanation:
, You know that for a collision to lead to a chemical reaction it must satisfy two criteria.
The collision must have sufficient energy for the reaction to occur. Also, the molecules
must be in the proper orientation for the collision to be effective. Therefore, not all
collisions result in a chemical reaction. Therefore choice (A) is incorrect.
The presence of a catalyst does increase the rate of a reaction. However, the way a
catalyst increases the rate of a reaction is not by making the collisions more effective.
Instead a catalyst increases the rate of a reaction by providing an alternative route from
reactants to products that has a smaller activation energy. Processes with smaller
activation energies result in a faster reaction rate. Therefore choice (B) is incorrect
Increasing the temperature often leads to an increase in the rate ofa reaction. However,
the reason is because as the temperature increases the average kinetic energy ofthe
reactants increases. This can increase the rate of a reaction in two ways. First, there
are more collisions that have the minimum energy needed for a reaction to occur.
Second, the higher kinetic energy increases the number of collisions, which means the
odds of a collision having the proper orientation increases. This increases the rate of a
reaction. Therefore choice (D) is incorrect.
Consider this equilibrium:
2SO2(g) +O2(g) --> 2SO3(g)
The forward reaction is proceeding at a certain rate at some temperature and pressure.
When the pressure is increased, what might we expect for the forward reaction?
Kinetics
a) a greater rate of reaction and a greater yield of SO3 at equilibrium
b) a greater rate of reaction and a same yield of SO3 at equilibrium
c) a lesser rate of reaction and a smaller yielf of SO3 at equlibrium
d) a lesser rate of reaction and a greater yield of S03 at equilibrium - Correct Answers -
a) a greater rate of reaction and a greater yield of SO3 at equilibrium
Explanation:
Le Chatlier's Principle
You know that a change in pressure may shift the equilibrium and depends on the
moles of gaseous substances as reactants and products. An increase in pressure will
shift the equilibrium in the direction that minimizes the increase in pressure. This is the
side that has the fewest moles of gas. For this reaction, the side with fewer moles of gas
is the product side. You realize that this means that an increase in pressure will cause
the rate of the reaction producing S03 to increase.
PQ-4: The gas phase reaction A2 + B2 --> 2AB, proceeds by bimolecular collisions
between A2 and B2 molecules. The rate law is rate=k[A2][B2]
If the concentrations of both A2 and B2 are doubled, the reaction rate will change by a
factor of
Kinetics
a) 1/2
