Question

A process has $\Delta H=200Jmo{l}^{-1}$ and $\Delta S=40J{K}^{-1}mo{l}^{-1}$. Out of the values given below, choose the minimum temperature above which the process will be spontaneous

• A. $20K$
• B. $4K$
• C. $5K$
• D. $12K$

Answer 1

Answer: (C)

$\Delta G=\Delta H-T\Delta S$
The process will be spontaneous, when
$\Delta G=-\text{ ve, i.e. }|T\Delta S|>|\Delta H|$
Given : $\Delta H=200Jmo{l}^{-1}$
and $\Delta S=40J{K}^{-1}mo{l}^{-1}$
$\Rightarrow T>\frac{|\Delta H|}{|\Delta S|}=\frac{200}{40}=5K$
So, the minimum temperature for spontaneity of the process is $5K$.