NEET 2025 MCQ with Answer Explanation : “Enthalpy, Entropy and Gibbs free energy”.

Here below some basic MCQ’s about enthalpy, entropy, gibbs free energy with answer and explanation. Which is given below.

1. Which of the following is a state function?
   a) Work
   b) Heat
   c) Enthalpy
   d) None of these
   Answer: c) Enthalpy

Explanation: Enthalpy (H) is a state function because it depends only on the state of the system, not on the path taken to reach that state.

2. The enthalpy change of a system is negative for:
   a) Endothermic reactions
   b) Exothermic reactions
   c) Isothermal processes
   d) Adiabatic processes
   Answer: b) Exothermic reactions

Explanation: In exothermic reactions, heat is released to the surroundings, causing a negative enthalpy change.

3. Which of the following describes entropy correctly?
   a) Measure of heat
   b) Measure of disorder
   c) Measure of work done
   d) Measure of temperature
   Answer: b) Measure of disorder

Explanation: Entropy (S) measures the disorder or randomness of a system. Greater entropy indicates more disorder.

4. The second law of thermodynamics states that in any spontaneous process:
   a) The entropy of the system remains constant
   b) The entropy of the universe increases
   c) The energy of the system decreases
   d) The enthalpy of the system increases
   Answer: b) The entropy of the universe increases

Explanation: According to the second law of thermodynamics, the total entropy of the universe always increases in a spontaneous process.

5. For a spontaneous process at constant temperature and pressure, the sign of Gibbs free energy (ΔG) should be:
   a) Positive
   b) Negative
   c) Zero
   d) Undefined
   Answer: b) Negative

Explanation: For a process to be spontaneous, the Gibbs free energy change (ΔG) must be negative.

6. Which of the following is true for an endothermic reaction?
   a) ΔH is negative
   b) ΔH is positive
   c) ΔS is always negative
   d) ΔS is always positive
   Answer: b) ΔH is positive

Explanation: In an endothermic reaction, the system absorbs heat, resulting in a positive enthalpy change (ΔH).

7. In a reversible process, which statement is correct?
   a) Entropy of the universe increases
   b) Entropy of the system increases
   c) Entropy of the system remains constant
   d) Entropy of the surroundings increases
   Answer: c) Entropy of the system remains constant

Explanation: In a reversible process, there is no net change in entropy for the system and surroundings.

8. Which of the following conditions are necessary for a reaction to be non-spontaneous?
   a) ΔG > 0
   b) ΔG = 0
   c) ΔG < 0 d) ΔS > 0
   Answer: a) ΔG > 0

Explanation: If Gibbs free energy (ΔG) is positive, the reaction is non-spontaneous under the given conditions.

9. Gibbs free energy (G) is related to enthalpy (H) and entropy (S) by the equation:
   a) ΔG = ΔH + TΔS
   b) ΔG = ΔH – TΔS
   c) ΔG = TΔH – S
   d) ΔG = ΔH + ΔS/T
   Answer: b) ΔG = ΔH – TΔS

Explanation: This is the Gibbs free energy equation, which relates the change in Gibbs energy to enthalpy (H), entropy (S), and temperature (T).

10. The entropy change for the evaporation of water at 100°C is:
    a) Positive
    b) Negative
    c) Zero
    d) Undefined
    Answer: a) Positive

Explanation: During evaporation, water molecules move from a more ordered liquid phase to a less ordered gaseous phase, thus increasing entropy.