Question

For a given reaction, $\Delta H=35.5kJmo{l}^{-1}$ and $\Delta S=83.6J{K}^{-1}mo{l}^{-1}$. The reaction is spontaneous at: (Assume that $\Delta H$ and $\Delta S$ do not vary with temperature)

• A. $T<425K$
• B. $T>425K$
• C. All temperatures
• D. $T>298K$

Answer 1

The correct option is B $T>425K$

$\because \Delta G=\Delta H-T\Delta S$
For a reaction to be spontaneous, $\Delta G$ = $–ve$
i.e., $\Delta H<T\Delta S$
$\therefore T>\frac{\Delta H}{\Delta S}=\frac{35.5\times {10}^{3}J}{83.6J{K}^{-1}}$
i.e., $T>425K$