Entropy MCQ – Objective Questions with Answers

Entropy MCQ – Objective Questions with Answers

Mechanical Engineering › Thermodynamics | Free practice MCQs with detailed explanations

Last Updated: June 2026

📌 About this MCQ Set

Entropy is a property of a system that measures molecular disorder and the unavailability of energy for doing work. It is central to the Second Law.

These MCQs cover the definition of entropy, entropy change in processes, and the principle of increase of entropy.

8 questions • every answer comes with a worked explanation. Click Show Answer to check yourself.

📖 New to this topic? Read the full concept guide: Entropy →

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Entropy MCQs

Q1. Entropy is a measure of:

  1. Energy content
  2. Molecular disorder / randomness
  3. Temperature
  4. Pressure
Show Answer

Answer: B. Molecular disorder / randomness

Entropy quantifies the disorder or randomness of a system and the unavailability of energy to do useful work.

Q2. Entropy is a:

  1. Path function
  2. Point (state) function
  3. Inexact differential
  4. Form of energy
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Answer: B. Point (state) function

Entropy depends only on the state of the system, so it is a point/state function.

Q3. The change in entropy for a reversible process is given by:

  1. dS = δQ_rev / T
  2. dS = δQ × T
  3. dS = T / δQ
  4. dS = δW / T
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Answer: A. dS = δQ_rev / T

For a reversible process dS = δQ_rev/T, where T is absolute temperature.

Q4. For an adiabatic reversible (isentropic) process, the entropy change is:

  1. Positive
  2. Negative
  3. Zero
  4. Maximum
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Answer: C. Zero

Reversible + adiabatic means δQ = 0 and reversible, so dS = 0 — the process is isentropic.

Q5. The entropy of an isolated system during a spontaneous process:

  1. Decreases
  2. Remains constant
  3. Increases
  4. Becomes negative
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Answer: C. Increases

The principle of increase of entropy: for any real process in an isolated system, entropy increases.

Q6. The units of specific entropy are:

  1. kJ/kg
  2. kJ/kg·K
  3. kJ
  4. kW/K
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Answer: B. kJ/kg·K

Specific entropy is energy per unit mass per unit absolute temperature: kJ/kg·K.

Q7. During heat addition at constant temperature, entropy change ΔS equals:

  1. Q/T
  2. QT
  3. T/Q
  4. Q − T
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Answer: A. Q/T

At constant temperature, ΔS = Q/T.

Q8. The Clausius inequality for a cyclic process is:

  1. ∮δQ/T = 0
  2. ∮δQ/T ≤ 0
  3. ∮δQ/T ≥ 0
  4. ∮δQ/T = 1
Show Answer

Answer: B. ∮δQ/T ≤ 0

For any cycle ∮δQ/T ≤ 0; equality holds only for a reversible cycle.

Frequently Asked Questions

What is entropy in simple terms?

Entropy measures the disorder or randomness of a system and how much of its energy is unavailable to do useful work.

Is entropy a path or state function?

Entropy is a state (point) function — it depends only on the current state, not the path taken.

Can entropy decrease?

The entropy of a specific system can decrease (e.g. cooling), but the total entropy of the universe never decreases for a real process.

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