21. The Second Law of Thermodynamics can also be expressed as:

• A) ΔU = Q – W
• B) ΔS ≥ 0 for spontaneous processes
• C) PV = nRT
• D) ΔH = ΔE + PΔV
• Answer: B

22. The Third Law of Thermodynamics is particularly relevant at:

• A) High temperatures
• B) Low temperatures
• C) Room temperature
• D) Standard temperature
• Answer: B

23. For an ideal gas, the entropy increases when:

• A) The temperature decreases
• B) The volume decreases
• C) The pressure increases
• D) The temperature increases
• Answer: D

24. Entropy change for a reversible adiabatic process is:

• A) Positive
• B) Negative
• C) Zero
• D) Constant but not zero
• Answer: C

25. Which of the following is a direct consequence of the Second Law of Thermodynamics?

• A) Energy is conserved
• B) Spontaneous processes increase the entropy of the universe
• C) The entropy of a perfect crystal is zero at absolute zero
• D) Work done is independent of path
• Answer: B

26. When a system undergoes an irreversible process, the total entropy:

• A) Increases
• B) Decreases
• C) Remains constant
• D) Becomes zero
• Answer: A

27. Which of the following processes is impossible according to the Second Law of Thermodynamics?

• A) Heat flowing from a hot object to a cold object
• B) Heat flowing from a cold object to a hot object without work
• C) Energy conversion with no loss
• D) Reversible processes
• Answer: B

28. The Clausius statement of the Second Law of Thermodynamics states that:

• A) No process is possible whose sole result is the transfer of heat from a colder body to a hotter body
• B) The total entropy of an isolated system remains constant
• C) Heat can be converted completely into work
• D) The entropy of a system approaches zero as temperature approaches zero
• Answer: A

29. Entropy change in an isolated system is:

• A) Always zero
• B) Always positive for spontaneous processes
• C) Always negative
• D) Unrelated to temperature
• Answer: B

30. Which of the following best represents a spontaneous process?

• A) Ice melting in a glass of warm water
• B) Water freezing in a freezer
• C) Air being pumped into a balloon
• D) A gas compressing in a piston
• Answer: A