In which of the following reaction standard entropy change (ΔS⁰) is positive and standard Gibb’s energy change (ΔG⁰) decreases sharply with increasing temperature

Options

(a) C (graphite) + 1/2 O₂(g) → CO(g)
(b) CO(g) + 1/2 O₂(g) → CO₂(g)
(c) Mg(s) + 1/2 O₂(g) → MgO(s)
(d) 1/2 C(graphite) + 1/2 O₂(g) → 1/2 CO₂(g)

Correct Answer:

C (graphite) + 1/2 O₂(g) → CO(g)

Explanation:

C(graphite) + 1/2 O₂(g) → CO(g),
Δn(g) = 1 – 1/2 = 1/2,
As amount of gaseous substance is increasing in product, thus
ΔS is positive for this reaction. And we know that ΔG = ΔH -TΔS. As ΔS is positive, thus increase in temperature will make TΔS more negative and ΔG will decrease.