Question

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

• A. $300K$
• B. $30K$
• C. $100K$
• D. ${300}^{o}C$

Answer 1

The correct option is A $300K$

Gibb's free energy equation : $\Delta G=\Delta H-T\Delta S$

For reaction to be spontaneous, $\Delta G<0$

$\therefore \Delta H-T\Delta S<0$

$\therefore (30\times {10}^3)-T\times \left(100\right)<0$

$\therefore 30000<100T$

$\therefore 300<T$

$\therefore T>300K$

Therefore, for reaction to be spontaneous, temperature should be above 300 K.