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 $\Delta Hand\Delta S$ do not vary with temperature.)

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

Answer 1

The correct option is A T > 425 K

For a spontaneous reaction,
$\Delta G<0i.e.,\Delta H-T\Delta S<0$
$T>\frac{\Delta H}{\Delta S}$
$T>(\frac{35.5\times 1000}{83.6}=424.6\approx 425K)$
$\therefore T>425K$