Question

During which of the following processes, does entropy decrease?


(A) Freezing of water to ice at 0°C

(B) Freezing of water to ice at -10°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

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

Answer 1

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

Answer: (a)

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 as we go from reactant to products. So, entropy decreases.

D → Adsorption will lead to a decrease in the randomness of gaseous particles.

$E\to NaCl\left(s\right)\to N{a}^{+}\left(aq\right)+C{l}^{–}\left(aq\right);\Delta S>0$
Here no of ions increase, so entropy increases.

So, (A, B, C, D) decreases entropy.