Question

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

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

Answer 1

Answer: (A)

T > 425 K

Answer 2

$\because \Delta G =\Delta H - T \Delta S$

For a reaction to be spontaneous, $\Delta G =- ve$

i.e., $\Delta H < T \Delta S$
$T >\frac{\Delta H }{\Delta S }=\frac{35.5 \times 10^{3} J }{83.6 JK ^{-1}}$

i.e., $T >425\, K$