Question

During which of the following processes, does entropy decrease?
(A) Freezing of water to ice at $0^{o}C$
(B) Freezing of water to ice at ${-10}^{o}C$
(C) $N_2\left(g\right)+3H_2\left(g\right)\to 2N{H}_3\left(g\right)$
(D) Adsorption of $CO\left(g\right)$ on lead surface
(E) Dissolution of $NaCl$ in water
Choose the correct answer from the options given below.

• A. (A) and (E) only
• B. (A), (C) and (E) only
• C. (A), (B), (C) and (D) only
• D. (B) and (C) only

Answer 1

The correct option is C (A), (B), (C) and (D) only

A, B → Freezing of water will decrease entropy as particles will move closer and forces of attraction will increase. This leads to a decrease in randomness. So, entropy decreases.

C → No. of molecules decreasing on product side so entropy decreases.

D → Adsorption will lead to a decrease in the randomness of gaseous particles. So, entropy decreases.

E → $NaCl\left(s\right)\to N{a}^{+}\left(aq\right)+C{l}^{–}\left(aq\right);\Delta S>0$

Hence, for (A, B, C, D) entropy will decrease.