,CHEM 104 Module 1 Exam General Chemistry II
w/Lab | Portage | 26/27|Q&A Actual (PDF)
1. Which statement accurately describes the relationship between entropy and spontaneity for an
isolated system?
A) A spontaneous process always results in a decrease in the system's entropy.
B) The entropy of an isolated system increases for spontaneous processes and remains constant for
reversible processes.
C) Spontaneous processes in an isolated system must be accompanied by an increase in the system's
enthalpy.
D) The entropy change of an isolated system is always zero for irreversible processes.
Correct Answer: The entropy of an isolated system increases for spontaneous processes and remains
constant for reversible processes.
Rationale: The second law of thermodynamics states that the entropy of an isolated system increases
in any spontaneous process and remains unchanged for a reversible process. Options A and C
contradict this foundational principle, while option D incorrectly asserts that irreversible processes
have zero entropy change in isolated systems.
2. For a reaction to be spontaneous at all temperatures, which combination of enthalpy and entropy
changes is required?
A) ΔH > 0 and ΔS > 0
B) ΔH < 0 and ΔS < 0
C) ΔH < 0 and ΔS > 0
,D) ΔH > 0 and ΔS < 0
Correct Answer: ΔH < 0 and ΔS > 0
Rationale: The Gibbs free energy equation, ΔG = ΔH - TΔS, dictates that a negative ΔH and a positive
ΔS will always yield a negative ΔG, making the reaction spontaneous at all temperatures. Options A
and B describe temperature-dependent spontaneity, while option D guarantees nonspontaneity
under all conditions.
3. A pure perfect crystalline solid at absolute zero (0 K) has an entropy of zero according to which law?
A) First law of thermodynamics
B) Second law of thermodynamics
C) Third law of thermodynamics
D) Zeroth law of thermodynamics
Correct Answer: Third law of thermodynamics
Rationale: The third law of thermodynamics states that the entropy of a perfect crystalline substance
at absolute zero is exactly zero. The first law concerns energy conservation, the second law addresses
entropy of the universe and spontaneity, and the zeroth law establishes thermal equilibrium as a basis
for temperature measurement.
4. Which process is expected to have a positive standard entropy change (ΔS° > 0)?
A) H2O(g) → H2O(l)
, B) 2 Na(s) + Cl2(g) → 2 NaCl(s)
C) N2(g) + 3 H2(g) → 2 NH3(g)
D) CaCO3(s) → CaO(s) + CO2(g)
Correct Answer: CaCO3(s) → CaO(s) + CO2(g)
Rationale: The decomposition of solid calcium carbonate into solid calcium oxide and carbon dioxide
gas increases the number of gaseous moles from zero to one, representing an increase in molecular
disorder and a positive ΔS°. Options A, B, and C all involve a decrease in the number of gaseous
species or increased order, leading to negative entropy changes.
5. What is the sign of ΔG for a nonspontaneous process at constant temperature and pressure?
A) Negative
B) Zero
C) Positive
D) Depends only on the enthalpy change
Correct Answer: Positive
Rationale: For a nonspontaneous process under standard conditions, the change in Gibbs free energy
is positive (ΔG > 0). A negative ΔG indicates spontaneity, while ΔG = 0 indicates equilibrium. The
enthalpy change alone is insufficient to determine spontaneity without considering temperature and
entropy.
6. The entropy of a system can be described as a measure of which of the following?
w/Lab | Portage | 26/27|Q&A Actual (PDF)
1. Which statement accurately describes the relationship between entropy and spontaneity for an
isolated system?
A) A spontaneous process always results in a decrease in the system's entropy.
B) The entropy of an isolated system increases for spontaneous processes and remains constant for
reversible processes.
C) Spontaneous processes in an isolated system must be accompanied by an increase in the system's
enthalpy.
D) The entropy change of an isolated system is always zero for irreversible processes.
Correct Answer: The entropy of an isolated system increases for spontaneous processes and remains
constant for reversible processes.
Rationale: The second law of thermodynamics states that the entropy of an isolated system increases
in any spontaneous process and remains unchanged for a reversible process. Options A and C
contradict this foundational principle, while option D incorrectly asserts that irreversible processes
have zero entropy change in isolated systems.
2. For a reaction to be spontaneous at all temperatures, which combination of enthalpy and entropy
changes is required?
A) ΔH > 0 and ΔS > 0
B) ΔH < 0 and ΔS < 0
C) ΔH < 0 and ΔS > 0
,D) ΔH > 0 and ΔS < 0
Correct Answer: ΔH < 0 and ΔS > 0
Rationale: The Gibbs free energy equation, ΔG = ΔH - TΔS, dictates that a negative ΔH and a positive
ΔS will always yield a negative ΔG, making the reaction spontaneous at all temperatures. Options A
and B describe temperature-dependent spontaneity, while option D guarantees nonspontaneity
under all conditions.
3. A pure perfect crystalline solid at absolute zero (0 K) has an entropy of zero according to which law?
A) First law of thermodynamics
B) Second law of thermodynamics
C) Third law of thermodynamics
D) Zeroth law of thermodynamics
Correct Answer: Third law of thermodynamics
Rationale: The third law of thermodynamics states that the entropy of a perfect crystalline substance
at absolute zero is exactly zero. The first law concerns energy conservation, the second law addresses
entropy of the universe and spontaneity, and the zeroth law establishes thermal equilibrium as a basis
for temperature measurement.
4. Which process is expected to have a positive standard entropy change (ΔS° > 0)?
A) H2O(g) → H2O(l)
, B) 2 Na(s) + Cl2(g) → 2 NaCl(s)
C) N2(g) + 3 H2(g) → 2 NH3(g)
D) CaCO3(s) → CaO(s) + CO2(g)
Correct Answer: CaCO3(s) → CaO(s) + CO2(g)
Rationale: The decomposition of solid calcium carbonate into solid calcium oxide and carbon dioxide
gas increases the number of gaseous moles from zero to one, representing an increase in molecular
disorder and a positive ΔS°. Options A, B, and C all involve a decrease in the number of gaseous
species or increased order, leading to negative entropy changes.
5. What is the sign of ΔG for a nonspontaneous process at constant temperature and pressure?
A) Negative
B) Zero
C) Positive
D) Depends only on the enthalpy change
Correct Answer: Positive
Rationale: For a nonspontaneous process under standard conditions, the change in Gibbs free energy
is positive (ΔG > 0). A negative ΔG indicates spontaneity, while ΔG = 0 indicates equilibrium. The
enthalpy change alone is insufficient to determine spontaneity without considering temperature and
entropy.
6. The entropy of a system can be described as a measure of which of the following?
