Question

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

• A. $C$ (graphite) $+\frac{1}{2} O _{2}( g ) \longrightarrow CO ( g )$
• B. $CO ( g )+\frac{1}{2} O _{2}( g ) \longrightarrow CO _{2}( g )$
• C. $Mg ( s )+\frac{1}{2} O _{2}( g ) \longrightarrow Mg O ( s )$
• D. $\frac{1}{-2} C$ (graphite) $+\frac{1}{2} O _{2}( g ) \longrightarrow \frac{1}{2} CO _{2}( g )$

Answer 1

Answer: (A)

$C$ (graphite) $+\frac{1}{2} O _{2}( g ) \rightarrow CO ( g )$
$\Delta S ^{\circ}$ is positive for this reaction because $0.5$ mole of gas on reactant side is giving one mole of gas on product side after reacting with $C$ (graphite).
Also $\Delta G$ decreases sharply with increase in temperature.