Physical Chemistry Exam Questions
And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A |
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1. Which thermodynamic quantity is a state function?
A. Heat
B. Work
C. Enthalpy
D. Path length
Answer: C. Enthalpy
Rationale: Enthalpy depends only on the initial and final states of a
system, so it is a state function. Heat and work depend on the path
taken between states.
2. The first law of thermodynamics is commonly expressed as:
A. ΔG = ΔH − TΔS
B. ΔU = q + w
C. ΔS = q/T
D. PV = nRT
Answer: B. ΔU = q + w
Rationale: The first law expresses conservation of energy. The change
in internal energy equals heat supplied to the system plus work done
on the system.
3. For an ideal gas undergoing free expansion into a vacuum, the
work done by the gas is:
,A. Positive
B. Negative
C. Zero
D. Equal to the enthalpy change
Answer: C. Zero
Rationale: In free expansion, the external pressure is zero. Since w =
−PextΔV, the work is zero even though the volume increases.
4. Which equation represents the ideal gas law?
A. PV = RT
B. P/V = nRT
C. PV = nRT
D. PT = nRV
Answer: C. PV = nRT
Rationale: The ideal gas law relates pressure, volume, amount, and
temperature through PV = nRT.
5. At constant pressure, the heat absorbed by a system is equal to its:
A. Internal energy change
B. Enthalpy change
C. Helmholtz energy change
D. Gibbs energy change
Answer: B. Enthalpy change
Rationale: At constant pressure with only pressure-volume work, q_p
= ΔH.
6. Which process has ΔU = 0 for an ideal gas?
A. Isothermal process
B. Isobaric process
,C. Isochoric process
D. Adiabatic process
Answer: A. Isothermal process
Rationale: The internal energy of an ideal gas depends only on
temperature. Therefore, at constant temperature, ΔU = 0.
7. An adiabatic process is one in which:
A. Temperature is constant
B. Pressure is constant
C. No heat is exchanged
D. Volume is constant
Answer: C. No heat is exchanged
Rationale: By definition, an adiabatic process has q = 0. Energy
changes through work and, where applicable, other forms of energy
transfer.
8. Which quantity is an extensive property?
A. Temperature
B. Pressure
C. Density
D. Volume
Answer: D. Volume
Rationale: Extensive properties depend on the amount of matter
present. Volume, mass, and total internal energy are examples.
9. Which quantity is an intensive property?
A. Mass
B. Volume
, C. Temperature
D. Number of moles
Answer: C. Temperature
Rationale: Intensive properties do not depend on the amount of
substance. Temperature, pressure, and density are intensive properties.
10. The zeroth law of thermodynamics establishes the concept
of:
A. Entropy
B. Temperature
C. Enthalpy
D. Chemical potential
Answer: B. Temperature
Rationale: The zeroth law states that if two systems are each in
thermal equilibrium with a third system, they are in thermal
equilibrium with each other. This provides the basis for defining
temperature.
11. For a reversible isothermal expansion of an ideal gas, the
work is:
A. w = −nRT ln(V₂/V₁)
B. w = nRT(V₂/V₁)
C. w = −PV
D. w = ΔU
Answer: A. w = −nRT ln(V₂/V₁)
Rationale: For reversible isothermal expansion of an ideal gas,
integrating w = −P dV with P = nRT/V gives w = −nRT ln(V₂/V₁).
12. In an isochoric process, which variable remains constant?
And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. Which thermodynamic quantity is a state function?
A. Heat
B. Work
C. Enthalpy
D. Path length
Answer: C. Enthalpy
Rationale: Enthalpy depends only on the initial and final states of a
system, so it is a state function. Heat and work depend on the path
taken between states.
2. The first law of thermodynamics is commonly expressed as:
A. ΔG = ΔH − TΔS
B. ΔU = q + w
C. ΔS = q/T
D. PV = nRT
Answer: B. ΔU = q + w
Rationale: The first law expresses conservation of energy. The change
in internal energy equals heat supplied to the system plus work done
on the system.
3. For an ideal gas undergoing free expansion into a vacuum, the
work done by the gas is:
,A. Positive
B. Negative
C. Zero
D. Equal to the enthalpy change
Answer: C. Zero
Rationale: In free expansion, the external pressure is zero. Since w =
−PextΔV, the work is zero even though the volume increases.
4. Which equation represents the ideal gas law?
A. PV = RT
B. P/V = nRT
C. PV = nRT
D. PT = nRV
Answer: C. PV = nRT
Rationale: The ideal gas law relates pressure, volume, amount, and
temperature through PV = nRT.
5. At constant pressure, the heat absorbed by a system is equal to its:
A. Internal energy change
B. Enthalpy change
C. Helmholtz energy change
D. Gibbs energy change
Answer: B. Enthalpy change
Rationale: At constant pressure with only pressure-volume work, q_p
= ΔH.
6. Which process has ΔU = 0 for an ideal gas?
A. Isothermal process
B. Isobaric process
,C. Isochoric process
D. Adiabatic process
Answer: A. Isothermal process
Rationale: The internal energy of an ideal gas depends only on
temperature. Therefore, at constant temperature, ΔU = 0.
7. An adiabatic process is one in which:
A. Temperature is constant
B. Pressure is constant
C. No heat is exchanged
D. Volume is constant
Answer: C. No heat is exchanged
Rationale: By definition, an adiabatic process has q = 0. Energy
changes through work and, where applicable, other forms of energy
transfer.
8. Which quantity is an extensive property?
A. Temperature
B. Pressure
C. Density
D. Volume
Answer: D. Volume
Rationale: Extensive properties depend on the amount of matter
present. Volume, mass, and total internal energy are examples.
9. Which quantity is an intensive property?
A. Mass
B. Volume
, C. Temperature
D. Number of moles
Answer: C. Temperature
Rationale: Intensive properties do not depend on the amount of
substance. Temperature, pressure, and density are intensive properties.
10. The zeroth law of thermodynamics establishes the concept
of:
A. Entropy
B. Temperature
C. Enthalpy
D. Chemical potential
Answer: B. Temperature
Rationale: The zeroth law states that if two systems are each in
thermal equilibrium with a third system, they are in thermal
equilibrium with each other. This provides the basis for defining
temperature.
11. For a reversible isothermal expansion of an ideal gas, the
work is:
A. w = −nRT ln(V₂/V₁)
B. w = nRT(V₂/V₁)
C. w = −PV
D. w = ΔU
Answer: A. w = −nRT ln(V₂/V₁)
Rationale: For reversible isothermal expansion of an ideal gas,
integrating w = −P dV with P = nRT/V gives w = −nRT ln(V₂/V₁).
12. In an isochoric process, which variable remains constant?
