In which of the following processes does entropy increase? A. A liquid evaporates to vapour. B. Temperature of a crystalline solid is lowered from $130\text{K}$ to $0\text{K}$. C. $2\mathrm{NaHCO}{}_3(\mathrm{s})\to \mathrm{Na}{}_2\mathrm{CO}{}_3(\mathrm{s})+\mathrm{CO}{}_2(\mathrm{g})+\mathrm{H}{}_2\mathrm{O}(\mathrm{g})$ D. $\mathrm{Cl}{}_2(\mathrm{g})\to 2\mathrm{Cl}(\mathrm{g})$ Choose the correct option:

Solution & Explanation

\textbf{Answer:} (B) A, C and D \textbf{Solution:} Entropy increases when randomness or the number of gaseous moles increases. A: liquid → vapour increases disorder, $\Delta S>0$. B: cooling a crystal toward $0\text{K}$ orders the lattice, $\Delta S<0$. C: $2\mathrm{NaHCO}{}_3(\mathrm{s})\to \mathrm{Na}{}_2\mathrm{CO}{}_3(\mathrm{s})+\mathrm{CO}{}_2(\mathrm{g})+\mathrm{H}{}_2\mathrm{O}(\mathrm{g})$ produces $2$ mol of gas from a solid, $\Delta S>0$. D: $\mathrm{Cl}{}_2(\mathrm{g})\to 2\mathrm{Cl}(\mathrm{g})$ increases the number of gaseous particles, $\Delta S>0$. Thus entropy increases for A, C and D. Mapped: source lowercase answer 'b' → option B.