Question

The values of $\Delta H$ and $\Delta S$ for a reaction are $30\, kJ\, mol ^{-1}$ and$100 \,JK ^{-1} mol ^{-1}$ respectively. Then the temperature above which the reaction will become spontaneous is

• A. $300\, K$
• B. $30\, K$
• C. $100\, K$
• D. $ 300^{\circ}C $

Answer 1

Answer: (A)

$ \because $ $ \Delta G=\Delta H-T.\Delta S $
$ \Delta G=30000-(T\times 100)\,J\,mol^{-1} $
For spontaneous process $\Delta G$ should be negative, i.e.,
$ \Delta G < 0 $
and this occurs when
$ T\Delta S>\Delta H. $
$ T>\frac{\Delta H}{\Delta S} $
$ T>\frac{30000}{100} $
$ T>300\,K $