In which of the following reactions, standard reaction entropy change ( S^o) is positive and standard Gibb's energy change ( G^o) decreases sharply with increasing temperature ?

A. C_ (graphite) , + ,1 2 O_ 2(g) , ,C O_ (g)

In which of the following reactions, standard reaction entropy ch…

MCQ

In which of the following reactions, standard reaction entropy change $(\Delta S^o)$ is positive and standard Gibb's energy change $(\Delta G^o)$ decreases sharply with increasing temperature ?

✓
${C_{(graphite)}}\, + \,\frac{1}{2}{O_{2(g)}}\, \to \,C{O_{(g)}}$
B
$C{O_{(g)}}\, + \,\frac{1}{2}{O_{2(g)}}\, \to \,C{O_{2(g)}}$
C
$M{g_{(s)}}\, + \,\frac{1}{2}{O_{2(g)}}\, \to \,Mg{O_{(s)}}$
D
$\frac{1}{2}{C_{(graphite)}}\, + \,\frac{1}{2}{O_{2(g)}}\, \to \,\,\frac{1}{2}C{O_{2(g)}}$

✓

Answer

Correct option: A.

${C_{(graphite)}}\, + \,\frac{1}{2}{O_{2(g)}}\, \to \,C{O_{(g)}}$

a
$\mathrm{C}_{(\text {graphite })}+\frac 12\mathrm{O}_{2(\mathrm{g})} \rightarrow \mathrm{CO}_{(\mathrm{g})}$

$\Delta n_{g}=1-\frac 12=\frac 12$

As amount of gaseous substance is increasing in product, thus $\Delta \mathrm{S}$ is positive for this reaction. And we know that $\Delta G=\Delta \mathrm{H} - T\Delta S$

As $\Delta \mathrm{S}$ is positive, thus increase in temperature will make $T\Delta S$ more negative and $\Delta \mathrm{G}$ will decrease.