Question 1

If ΔG < 0 for a reaction, then the reaction is said to be:
A) endothermic
B) reversible
C) spontaneous
D) exothermic
E) fast

Accepted Answer

If ΔG < 0, it means that the change in free energy is negative and the reaction will have a spontaneous tendency to occur.

Question 2

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?
A) ΔH+, ΔS-
B) ΔH-, ΔS+
C) ΔH-, ΔS-
D) ΔH+, ΔS+
E) cannot determine without temperature

Accepted Answer

A positive ΔH means the reaction is endothermic and absorbs heat, which is not favorable for spontaneity. A negative ΔS means the system becomes more ordered, which is also not favorable for spontaneity. Therefore, the combination of ΔH+ and ΔS- will always result in a non-spontaneous reaction.

Question 3

Which of the following has the largest molar entropy? A) I₂(g) B) Xe(g) C) H₂(g) D) He(g)

Accepted Answer

Iodine gas (I2) has the largest molar entropy because it is a diatomic molecule with more complex structure and more degrees of freedom compared to the monoatomic gases Xe, H2, and He.

Question 4

Choose the INCORRECT statement.
A) The third law of thermodynamics states that the entropy of a pure crystal at 298 K is zero.
B) ΔS° = Σ (ν S°) products - Σ (ν S°) reactants.
C) The activity of pure liquids or pure solids is 1.
D) ΔG° = -RT ln Keq.
E) ΔG° = ΔH° - TΔS°.

Accepted Answer

The third law of thermodynamics states that the entropy of a pure crystal at absolute zero (0 K) is zero, not at 298 K.

Question 5

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be ________ while the entropy is ________.
A) positive, also positive
B) positive, negative
C) a relatively small negative value, also negative
D) a relatively large negative value, positive
E) a very large negative value, also negative

Accepted Answer

For an exothermic reaction to be non-spontaneous at high temperatures, the enthalpy change must be negative (indicating it releases heat), and the entropy change must also be negative (indicating a decrease in disorder). This combination can lead to a situation where, at high temperatures, the TΔS term in the Gibbs free energy equation (ΔG = ΔH - TΔS) becomes large enough to make ΔG positive, thus making the reaction non-spontaneous.

Question 6

If ΔG is positive for a certain reaction, then:
A) the reaction is spontaneous.
B) the reverse of the reaction is spontaneous.
C) the system is in equilibrium.
D) one would need to know the Kelvin temperature to determine spontaneity.
E) there would be no reaction possible for a negative value.

Accepted Answer

If ΔG is positive, it means that the forward reaction is not spontaneous. However, the reverse reaction can still be spontaneous as the sign of ΔG would be negative for the reverse reaction. Therefore, option B is the best choice.

Question 7

The normal melting and boiling points of SO₂ are 198 and 263 K, respectively. For a plot of the standard molar entropy of SO₂ versus temperature, which of the following is INCORRECT? A) At 263 K, S° is constant. B) S° increases with increasing temperature. C) S° equals zero at 0 K. D) At 198 K, S° increases by the value of △Sfusion.

Accepted Answer

At 263 K, SO2 is undergoing a phase change from liquid to gas, so the standard molar entropy (S°) increases by the value of △Svaporization, not constant.

Question 8

The maximum quantity of energy available for useful work is:
A) constant
B) Gibbs energy
C) the entropy
D) the internal energy
E) the enthalpy

Accepted Answer

Gibbs energy (or Gibbs free energy) is the maximum amount of energy available to do useful work at constant temperature and pressure.

Question 9

The change in Gibbs energy for a reaction:
A) = ΔH - TΔS
B) = Q (heat)
C) = ΔS + TΔH
D) = ΔS - TΔH
E) = ΔH + TΔS

Accepted Answer

The change in Gibbs energy (ΔG) for a reaction is given by the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

Question 10

The Gibbs energy change for a reaction is -298 kJ. The reaction is therefore:
A) exothermic
B) irreversible
C) spontaneous
D) endothermic
E) nonspontaneous

Accepted Answer

The answer of The Gibbs energy change for a reaction...

Question 11

Which of the following best expresses the increased degree of randomness associated with melting and sublimation, respectively?
A) ΔSfus - ΔSsub = 0
B) ΔSfus = 144.3 J/mol-K, ΔSsub = 9.0 J/mol-K
C) ΔSfus = 9.0 J/mol-K, ΔSsub = -144.3 J/mol-K
D) ΔH for both processes is zero
E) ΔSfus = 9.0 J/mol-K, ΔSsub = 144.3 J/mol-K

Accepted Answer

The increased degree of randomness associated with melting and sublimation is expressed by the ΔS value of each process. ΔS represents the change in entropy. Entropy is a measure of the degree of disorder or randomness in a system.

Melting increases the degree of randomness because the solid state has a more ordered arrangement of molecules than the liquid state. Therefore, the ΔS value for melting is expected to be positive.

Sublimation also increases the degree of randomness because the solid state has a more ordered arrangement of molecules than the gaseous state. Therefore, the ΔS value for sublimation is expected to be positive.

The only choice that reflects an increase in randomness associated with both melting and sublimation is E, where ΔSfus is 9.0 J/mol-K, and ΔSsub is 144.3 J/mol-K.

Question 12

Which of the following relations is true for the molar entropy of sublimation of a substance?
A) ΔSsub = ΔSfusion + ΔSvaporization
B) ΔSsub < ΔSvaporization
C) ΔSsub = ΔSfusion - ΔSvaporization
D) ΔSsub < (ΔSfusion + ΔSvaporization)

Accepted Answer

The molar entropy of sublimation (ΔSsub) is the sum of the molar entropy of fusion (ΔSfusion) and the molar entropy of vaporization (ΔSvaporization), as sublimation is the direct transition from solid to gas.

Question 13

Which of the following substances under equal conditions and in the same phase has the greatest molar entropy? A) NO B) NO₂ C) N₂O₃ D) N₂O₄ E) N₂O₅

Accepted Answer

As the number of atoms in a molecule increases, the molar entropy also increases. Among the given options, E has the highest number of atoms and therefore the highest molar entropy. The presence of multiple sulfur and oxygen atoms also contributes to a higher molar entropy.

Question 14

In a sealed container, the rate of dissolving is equal to the rate of crystallization. Therefore we would expect:
A) ΔG < 0
B) ΔG > 0
C) ΔG = 0
D) ΔS = 0
E) must know ΔH to determine

Accepted Answer

In a sealed container, the system is at equilibrium, which means there is no net change in the amount of dissolved solute or crystallized solute. This indicates that ΔG (free energy change) is equal to zero.

Question 15

A reaction is spontaneous if: 
I. ΔG is a negative value
II. both enthalpy and entropy increase
III. ΔH is negative and ΔS is positive
IV. both enthalpy and entropy decrease
V. ΔH is positive and ΔS is negative
A) I and III
B) I and II
C) II and V
D) III and IV
E) II and IV

Accepted Answer

A reaction is spontaneous if ΔG is negative, which is stated in option I. A negative ΔG implies that the reaction is exergonic and can proceed spontaneously. Additionally, option III is also correct because if ΔH is negative and ΔS is positive, it will also result in a negative ΔG, making the reaction spontaneous. Option II, IV, and V are incorrect as they do not guarantee that the reaction will be spontaneous.

Question 16

The following reaction is exothermic. 2N₂O(g) → 2N₂(g) + O₂(g) This means the reaction: A) will be spontaneous at all temperatures B) will be spontaneous only at high temperature C) will be spontaneous only at low temperatures D) is not spontaneous at any temperature

Accepted Answer

The fact that the reaction is exothermic means that it releases heat, which is a driving force for spontaneous reactions. Therefore, the reaction will be spontaneous at all temperatures.

Question 17

The following reaction is endothermic. 2NH₃(g) → N₂(g) + 3H₂(g) This means the reaction: A) will be spontaneous at high temperature B) will be spontaneous at low temperature C) is not spontaneous at any temperature D) is spontaneous at all temperatures

Accepted Answer

An endothermic reaction absorbs heat, so increasing the temperature can make it spontaneous by providing the necessary energy to overcome the enthalpy change.

Question 18

The change in Gibbs energy of a reaction:
A) = work
B) predicts speed
C) = ΔH + TΔS
D) depends on the standard state chosen
E) tells us if the reaction is spontaneous or not

Accepted Answer

The answer of The change in Gibbs energy of a...

Question 19

Choose the INCORRECT statement.
A) One form of the second law of thermodynamics is all spontaneous processes produce an increase in the entropy of the universe.
B) Gibbs energy is defined by: G = H - TS.
C) If ΔG < 0, the process is spontaneous.
D) If ΔG > 0, the process is nonspontaneous.
E) If ΔG = 0, the process is spontaneous.

Accepted Answer

If ΔG = 0, the process is at equilibrium, not spontaneous.

Question 20

The fact that the entropies of vaporization for liquids which exhibit hydrogen bonding are greater than the 87 J/(mol ∙ K) which is expected of non-polar liquids is an exception to:
A) the Gibb's Energy Rule
B) the Third Law of Thermodynamics
C) the Clausius-Clapyeron Rule
D) the Second Law of Thermodynamics
E) Trouton's Rule

Accepted Answer

Trouton's Rule states that the entropy of vaporization for most liquids is approximately 87 J/(mol ∙ K). Liquids with hydrogen bonding have higher entropies of vaporization, which is an exception to this rule.

Quiz 19: Spontaneous Change: Entropy and Free Energy

If ΔG < 0 for a reaction, then the reaction is said to be:

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?

Which of the following has the largest molar entropy?

Choose the INCORRECT statement.

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be while the entropy is .

If ΔG is positive for a certain reaction, then:

The normal melting and boiling points of SO₂ are 198 and 263 K, respectively. For a plot of the standard molar entropy of SO₂ versus temperature, which of the following is INCORRECT?

The maximum quantity of energy available for useful work is:

The change in Gibbs energy for a reaction:

The Gibbs energy change for a reaction is -298 kJ. The reaction is therefore:

Which of the following best expresses the increased degree of randomness associated with melting and sublimation, respectively?

Which of the following relations is true for the molar entropy of sublimation of a substance?

Which of the following substances under equal conditions and in the same phase has the greatest molar entropy?

In a sealed container, the rate of dissolving is equal to the rate of crystallization. Therefore we would expect:

A reaction is spontaneous if: I. ΔG is a negative value II. both enthalpy and entropy increase III. ΔH is negative and ΔS is positive IV. both enthalpy and entropy decrease V. ΔH is positive and ΔS is negative

The following reaction is exothermic. 2N₂O(g) → 2N₂(g) + O₂(g) This means the reaction:

The following reaction is endothermic. 2NH₃(g) → N₂(g) + 3H₂(g) This means the reaction:

The change in Gibbs energy of a reaction:

Choose the INCORRECT statement.

The fact that the entropies of vaporization for liquids which exhibit hydrogen bonding are greater than the 87 J/(mol ∙ K) which is expected of non-polar liquids is an exception to:

Quiz 19: Spontaneous Change: Entropy and Free Energy

If ΔG < 0 for a reaction, then the reaction is said to be:

Which of the following combinations of signs for ΔH and ΔS will always result in a reaction being nonspontaneous?

Which of the following has the largest molar entropy?

Choose the INCORRECT statement.

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be ________ while the entropy is ________.

If ΔG is positive for a certain reaction, then:

The normal melting and boiling points of SO2 are 198 and 263 K, respectively. For a plot of the standard molar entropy of SO2 versus temperature, which of the following is INCORRECT?

The maximum quantity of energy available for useful work is:

The change in Gibbs energy for a reaction:

The Gibbs energy change for a reaction is -298 kJ. The reaction is therefore:

Which of the following best expresses the increased degree of randomness associated with melting and sublimation, respectively?

Which of the following relations is true for the molar entropy of sublimation of a substance?

Which of the following substances under equal conditions and in the same phase has the greatest molar entropy?

In a sealed container, the rate of dissolving is equal to the rate of crystallization. Therefore we would expect:

A reaction is spontaneous if: I. ΔG is a negative value II. both enthalpy and entropy increase III. ΔH is negative and ΔS is positive IV. both enthalpy and entropy decrease V. ΔH is positive and ΔS is negative

The following reaction is exothermic. 2N2O(g) → 2N2(g) + O2(g) This means the reaction:

The following reaction is endothermic. 2NH3(g) → N2(g) + 3H2(g) This means the reaction:

The change in Gibbs energy of a reaction:

Choose the INCORRECT statement.

The fact that the entropies of vaporization for liquids which exhibit hydrogen bonding are greater than the 87 J/(mol ∙ K) which is expected of non-polar liquids is an exception to:

For an exothermic reaction to be nonspontaneous at high temperatures, the enthalpy must be while the entropy is .

The normal melting and boiling points of SO₂ are 198 and 263 K, respectively. For a plot of the standard molar entropy of SO₂ versus temperature, which of the following is INCORRECT?

The following reaction is exothermic. 2N₂O(g) → 2N₂(g) + O₂(g) This means the reaction:

The following reaction is endothermic. 2NH₃(g) → N₂(g) + 3H₂(g) This means the reaction: