MCAT GENERAL CHEMISTRY EXAM QUESTIONS WITH
COMPLETE SOLUTIONS
1) All of the following are forms of internal energy EXCEPT:
A) rotational energy
B) vibrational energy
C) gravitational energy
D) translational energy -- Correct Answer ✔✔ C) gravitational energy
Internal energy is the energy of molecules on a microscopic scale -- all forms of
energy excluding those related to the motion of the system as a whole.
Gravitational energy is an example of potential energy at the macroscopic level, not
the microscopic level.
2) Which of the following is a type of kinetic energy?
A) vibrational energy
B) chemical energy
C) rest mass energy
D) intermolecular energy -- Correct Answer ✔✔ A) vibrational energy
3) As the temperature of hydrogen gas in a sealed container is increased, which of the
following occurs?
A) a decrease in the random translational energy, decreasing pressure
B) a decrease in the random translational energy, increasing pressure
C) an increase in the random translational energy, decreasing pressure
D) an increase in the random translational energy, increasing pressure --
Correct Answer ✔✔ D) an increase in the random translational energy,
increasing pressure
, The kinetic energy of molecules of a gas is directly proportional to temperature, as
given by KE = 3/2RT. Therefore, increasing temperature will increase the random
translational energy of the gas molecules, eliminating A and B. If the molecules have
a higher kinetic energy, they would be moving faster, hitting the walls of the
container more frequently, causing an increase in pressure. Another way to
determine the effect of temperature on pressure is to use the ideal gas law (PV =
nRT). Increasing the temperature while holding the volume constant would cause
the pressure to increase, eliminating choice C.
4) For a particular reversible reaction, the forward process is exothermic and the
reverse process is endothermic. Which of the following statements must be true
about this reaction?
A) the forward reaction will be spontaneous under standard conditions
B) the reverse reaction will be spontaneous under standard conditions
C) the activation energy will be greater for the forward reaction than for the
reverse reaction
D) the activation energy will be greater for the reverse reaction than for the
forward reaction -- Correct Answer ✔✔ D) the activation energy will be
greater for the reverse reaction than for the forward reaction
Activation energy is greater for an endothermic reaction than for an exothermic
reaction.
5) Sulfur dioxide reacts with oxygen in a reversible reaction to form sulfur trioxide
(2SO2 + O2 --> 2SO3) with standard enthalpy of formation of -200 kJ/mol. If the
temperature at which the reaction takes place is increased, which of the following
will occur?
A) the rates of the forward and reverse reactions will increase
B) only the rate of the forward reaction will increase
C) only the rate of the reverse reaction will increase
D) the rates of neither the forward nor reverse reactions will increase --
Correct Answer ✔✔ A) the rates of the forward and reverse reactions
will increase
Increasing the temperature increases the energy available to both the forward and
reverse reactions, enabling both to more easily overcome the activation energy. As
a note, the rate of the reverse reaction will increase more than the rate of the
, forward reaction. This is because the reaction is exothermic, making heat a
product. Based on Le Chatelier's principle, an increase in temperature (heat) will
cause a leftward shift by increasing the reverse rate of reaction more than the
forward rate.
6) Which of the following describes a reaction that is always spontaneous?
A) increasing enthalpy and increasing entropy
B) decreasing enthalpy and decreasing entropy
C) increasing enthalpy and decreasing entropy
D) decreasing enthalpy and increasing entropy -- Correct Answer ✔✔ D)
decreasing enthalpy and increasing entropy
According to the reaction given by Gibbs free energy, ΔG = ΔH-TΔS, a reaction will
be spontaneous (ΔG < 0) if the enthalpy of the system decreases (ΔH < 0) and the
entropy of the system increases (ΔS > 0)
7) Which of the following statements about entropy is false?
A) the entropy of a system will always increase in a spontaneous reaction
B) entropy is a measure of disorder
C) the entropy change of a forward reaction is exactly opposite to the
entropy change of the reverse reaction
D) entropy increases with temperature -- Correct Answer ✔✔ A) the
entropy of a system will always increase in a spontaneous reaction
The entropy of the universe will increase in a spontaneous reaction, but the
entropy of a system may or may not increase. Entropy increases with number,
volume, and temperature (all allow for increased disorder). Additionally, the
entropy change for the reverse reaction is the opposite sign of the entropy change
for the forward reaction of the system because entropy is a state function.
8) The condensation of water is shown. H2O (g) --> H2O (l). Which of the following
will be positive for the condensation of water at 25 degrees C and 1 atm?
A) ΔH
B) ΔS
C) ΔG
D) none of the above -- Correct Answer ✔✔ D) none of the above
, Bonds are formed when water condenses, so energy is released and ΔH is negative.
The water molecules become less random, so ΔS is negative. Condensation occurs
spontaneously at 25 degrees C (water is a liquid at room temperature), so ΔG is
negative. Notice that this question can be answered without any numbers.
9) AgCl (s) --> Ag+ (aq) + Cl- (aq). During the course of this reaction, both entropy
and enthalpy are increased. If the reaction is not spontaneous at a given temperature
and pressure, what can be done to make the reaction occur spontaneously?
A) increase the temperature
B) decrease the temperature
C) increase the pressure
D) decrease the pressure -- Correct Answer ✔✔ A) increase the
temperature
ΔG = ΔH - TΔS. For a spontaneous reaction, ΔG must be negative. ΔH > 0 and ΔS
< 0 for the reaction given. In order for ΔG to be negative, an increase in
temperature will increase the negative term of the equation, -TΔS. If T is increased
enough, ΔG will eventually switch from positive to negative. Changing the pressure
will have no effect on a nongaseous reaction that takes place in a solution.
10) All of the following are true concerning a reaction at equilibrium EXCEPT:
A) the rate of the forward reaction equals the rate of the reverse reaction
B) there is no change in the concentrations of either products or reactants
C) the activation energy has reached zero
D) the Gibbs free energy has reached a minimum -- Correct Answer ✔✔ C)
the activation energy has reached zero
Equilibrium is defined as the condition where the forward reaction rate equals the
reverse reaction rate, eliminating choice A. Although reactants and products are
being formed and consumed at equilibrium, there is no change in their
concentrations, eliminating choice B. Gibbs free energy is given by ΔG = ΔG* +
RTln(Q), where Q = K at equilibrium. Therefore ΔG = 0 and is a minimum at
equilibrium, eliminating choice D. The activation energy is a property of the
reaction itself and does not change during the reaction, making C the best answer.
COMPLETE SOLUTIONS
1) All of the following are forms of internal energy EXCEPT:
A) rotational energy
B) vibrational energy
C) gravitational energy
D) translational energy -- Correct Answer ✔✔ C) gravitational energy
Internal energy is the energy of molecules on a microscopic scale -- all forms of
energy excluding those related to the motion of the system as a whole.
Gravitational energy is an example of potential energy at the macroscopic level, not
the microscopic level.
2) Which of the following is a type of kinetic energy?
A) vibrational energy
B) chemical energy
C) rest mass energy
D) intermolecular energy -- Correct Answer ✔✔ A) vibrational energy
3) As the temperature of hydrogen gas in a sealed container is increased, which of the
following occurs?
A) a decrease in the random translational energy, decreasing pressure
B) a decrease in the random translational energy, increasing pressure
C) an increase in the random translational energy, decreasing pressure
D) an increase in the random translational energy, increasing pressure --
Correct Answer ✔✔ D) an increase in the random translational energy,
increasing pressure
, The kinetic energy of molecules of a gas is directly proportional to temperature, as
given by KE = 3/2RT. Therefore, increasing temperature will increase the random
translational energy of the gas molecules, eliminating A and B. If the molecules have
a higher kinetic energy, they would be moving faster, hitting the walls of the
container more frequently, causing an increase in pressure. Another way to
determine the effect of temperature on pressure is to use the ideal gas law (PV =
nRT). Increasing the temperature while holding the volume constant would cause
the pressure to increase, eliminating choice C.
4) For a particular reversible reaction, the forward process is exothermic and the
reverse process is endothermic. Which of the following statements must be true
about this reaction?
A) the forward reaction will be spontaneous under standard conditions
B) the reverse reaction will be spontaneous under standard conditions
C) the activation energy will be greater for the forward reaction than for the
reverse reaction
D) the activation energy will be greater for the reverse reaction than for the
forward reaction -- Correct Answer ✔✔ D) the activation energy will be
greater for the reverse reaction than for the forward reaction
Activation energy is greater for an endothermic reaction than for an exothermic
reaction.
5) Sulfur dioxide reacts with oxygen in a reversible reaction to form sulfur trioxide
(2SO2 + O2 --> 2SO3) with standard enthalpy of formation of -200 kJ/mol. If the
temperature at which the reaction takes place is increased, which of the following
will occur?
A) the rates of the forward and reverse reactions will increase
B) only the rate of the forward reaction will increase
C) only the rate of the reverse reaction will increase
D) the rates of neither the forward nor reverse reactions will increase --
Correct Answer ✔✔ A) the rates of the forward and reverse reactions
will increase
Increasing the temperature increases the energy available to both the forward and
reverse reactions, enabling both to more easily overcome the activation energy. As
a note, the rate of the reverse reaction will increase more than the rate of the
, forward reaction. This is because the reaction is exothermic, making heat a
product. Based on Le Chatelier's principle, an increase in temperature (heat) will
cause a leftward shift by increasing the reverse rate of reaction more than the
forward rate.
6) Which of the following describes a reaction that is always spontaneous?
A) increasing enthalpy and increasing entropy
B) decreasing enthalpy and decreasing entropy
C) increasing enthalpy and decreasing entropy
D) decreasing enthalpy and increasing entropy -- Correct Answer ✔✔ D)
decreasing enthalpy and increasing entropy
According to the reaction given by Gibbs free energy, ΔG = ΔH-TΔS, a reaction will
be spontaneous (ΔG < 0) if the enthalpy of the system decreases (ΔH < 0) and the
entropy of the system increases (ΔS > 0)
7) Which of the following statements about entropy is false?
A) the entropy of a system will always increase in a spontaneous reaction
B) entropy is a measure of disorder
C) the entropy change of a forward reaction is exactly opposite to the
entropy change of the reverse reaction
D) entropy increases with temperature -- Correct Answer ✔✔ A) the
entropy of a system will always increase in a spontaneous reaction
The entropy of the universe will increase in a spontaneous reaction, but the
entropy of a system may or may not increase. Entropy increases with number,
volume, and temperature (all allow for increased disorder). Additionally, the
entropy change for the reverse reaction is the opposite sign of the entropy change
for the forward reaction of the system because entropy is a state function.
8) The condensation of water is shown. H2O (g) --> H2O (l). Which of the following
will be positive for the condensation of water at 25 degrees C and 1 atm?
A) ΔH
B) ΔS
C) ΔG
D) none of the above -- Correct Answer ✔✔ D) none of the above
, Bonds are formed when water condenses, so energy is released and ΔH is negative.
The water molecules become less random, so ΔS is negative. Condensation occurs
spontaneously at 25 degrees C (water is a liquid at room temperature), so ΔG is
negative. Notice that this question can be answered without any numbers.
9) AgCl (s) --> Ag+ (aq) + Cl- (aq). During the course of this reaction, both entropy
and enthalpy are increased. If the reaction is not spontaneous at a given temperature
and pressure, what can be done to make the reaction occur spontaneously?
A) increase the temperature
B) decrease the temperature
C) increase the pressure
D) decrease the pressure -- Correct Answer ✔✔ A) increase the
temperature
ΔG = ΔH - TΔS. For a spontaneous reaction, ΔG must be negative. ΔH > 0 and ΔS
< 0 for the reaction given. In order for ΔG to be negative, an increase in
temperature will increase the negative term of the equation, -TΔS. If T is increased
enough, ΔG will eventually switch from positive to negative. Changing the pressure
will have no effect on a nongaseous reaction that takes place in a solution.
10) All of the following are true concerning a reaction at equilibrium EXCEPT:
A) the rate of the forward reaction equals the rate of the reverse reaction
B) there is no change in the concentrations of either products or reactants
C) the activation energy has reached zero
D) the Gibbs free energy has reached a minimum -- Correct Answer ✔✔ C)
the activation energy has reached zero
Equilibrium is defined as the condition where the forward reaction rate equals the
reverse reaction rate, eliminating choice A. Although reactants and products are
being formed and consumed at equilibrium, there is no change in their
concentrations, eliminating choice B. Gibbs free energy is given by ΔG = ΔG* +
RTln(Q), where Q = K at equilibrium. Therefore ΔG = 0 and is a minimum at
equilibrium, eliminating choice D. The activation energy is a property of the
reaction itself and does not change during the reaction, making C the best answer.
