Question

In which case is the change in entropy negative?

• A. Evaporation of water
• B. Expansion of a gas at constant temperature
• C. Sublimation of solid to gas
• D. $2H\left(g\right)$ $⟶$$H_2\left(g\right)$

Answer 1

The correct option is D $2H\left(g\right)$ $⟶$$H_2\left(g\right)$

Entropy is a measure of randomness.

a) During evaporation, the state of water is changing from liquid to gas, thus the entropy increases.

b) When a gas expands at constant temperature, the constituent particles to move more freely and hence the entropy increases.

c) During sublimation, the physical state is changing from solid to gas, thus the randomness increases and accordingly entropy increases.
d) In the reaction, $2H\left(g\right)$ $⟶$$H_2\left(g\right)$, change in entropy is negative as $△$$n_g<0$.