Which one of the following has ΔS° greater than zero?
(a) CaO(s) + CO2(g) ⇌ CaCO3
(b) NaCl(aq) ⇌ NaCl(s)
(c) NaNO3(s) ⇌ Na+(aq) + NO-3(aq)
(d) N2(g) + 3H2(g) ⇌ 2NH3(g)
(c) NaNO3(s) ⇌ Na+(aq) + NO-3(aq)
Explanation:
Entropy (ΔS) of a reaction is positive if the products are in more random state as compared to reactants. Order of randomness : Gas > Liquid > Solid
(i) In (b), product NaCl (solid) has lesser entropy as compared to NaCl (aq) (Na+ and Cl-) in reactant.
(ii) In (a), product (solid) has lesser entropy as compared to reactants.
(iii) In (d), both reactants and products are in gaseous state, but number of moles of products are decreasing.
(iv) In (c), products are in liquid state hence high entropy than reactant which is present in solid state.