Question

For a particular reaction, $\Delta H^o=-33.9kJand\Delta S^o=-113J{K}^{-1}mo{l}^{-1}$. This reaction is:

• A. Spontaneous at all temperatures
• B. Non-spontaneous at all temperatures
• C. Spontaneous at temperatures below $27{}^{o}C$
• D. Spontaneous at temperatures above $27{}^{o}C$

Answer 1

The correct option is C Spontaneous at temperatures below $27{}^{o}C$

By using relation,
$\Delta G=\Delta H-T\Delta S$
We know that,
For a process at equilibrium
$\Delta G=0$
$\Rightarrow \Delta H-T\Delta S=0$
$\Rightarrow \frac{\Delta H}{\Delta S}=T$
Substituting the values, we get
$\Rightarrow \frac{(-33.9\times 1000)}{-113}=T$
$\Rightarrow T=300K,i.e.27{}^{o}C$
For the process to be spontaneous, temperature must be less than 300 K