Question

$△H$ and $△S$ for the reaction: $A{g}_{2}O\left(s\right)\to 2Ag\left(s\right)+\frac{1}{2}{O}_2\left(g\right)$ are 30.56 kJ $mo{l}^{-1}$ and 66.0 J $K^{-1}mo{l}^{-1}$ respectively. Calculate the temperature at which free energy change for the reaction will be zero. Predict whether the forward reaction will be favored above or below this temperature.

• A. 298 K, above
• B. 300 K, below
• C. 373 K, above
• D. 463 K, above

Answer 1

The correct option is D

463 K, above

We know that, $△G=△H-T△S$
At equilibrium, $△G$ = 0
So that 0 = $△H-T△S$
or $T=\frac{△H}{△S}$
given that $△H$ - 30.56 kJ $mo{l}^{-1}$ = 30560 J $mo{l}^{-1}$
$△S$ = 66.0 J $K^{-1}mo{l}^{-1}$
T = $\frac{30560}{66}$ = 463 K
Above this temperature, $△G$ will be negative and the process will be spontaneous in forward direction.