Question

In which of the following processes entropy increases?
A. A liquid evaporates to vapour.
B. Temperature of a crystalline solid lowered from 130 K to 0 K.
C. 2NaHCO₃(s) → Na₂CO₃(s)+CO₂(g)+H₂O(g)
D. Cl₂(g) → 2Cl(g)
Choose the correct answer from the options given below:

• A. A and C
• B. A, B and D
• C. A, C and D
• D. C and D

Answer 1

The Correct Option is C

To identify processes where entropy increases, we first define entropy as a measure of system disorder or randomness. Entropy typically rises when the number of possible system states or configurations expands. Let us examine each process:

1. A. A liquid evaporates to vapour.
   Evaporation converts a liquid to a gas. Gases exhibit greater disorder than liquids due to the increased freedom of molecular motion and larger volume occupied by gas molecules. Consequently, entropy increases.
2. B. Temperature of a crystalline solid lowered from 130 K to 0 K.
   Reducing the temperature of a solid generally decreases its entropy by diminishing molecular motion, resulting in a more ordered system.
3. C. \(2\text{NaHCO}_3(s) \rightarrow \text{Na}_2\text{CO}_3(s)+\text{CO}_2(g)+\text{H}_2\text{O}(g)\)
   This chemical reaction involves the decomposition of solid sodium bicarbonate into solid sodium carbonate, carbon dioxide gas, and water vapor. The generation of gases from a solid substantially increases entropy due to the inherent higher disorder of gases.
4. D. \(\text{Cl}_2(g) \rightarrow 2\text{Cl}(g)\)
   The dissociation of chlorine gas into chlorine atoms leads to an increase in entropy. Although both substances are gaseous, the creation of more particles (from one mole of \(\text{Cl}_2\) to two moles of \(\text{Cl}\)) results in greater disorder.

Accordingly, the processes demonstrating increased entropy are: A, C, and D