Thermodynamics and Thermochemistry - Result Question 17
17. A process has $\Delta H=200 \mathrm{~J} \mathrm{~mol}^{-1}$ and $\Delta S=40 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$. Out of the values given below, choose the minimum temperature above which the process will be spontaneous
(2019 Main, 10 Jan I)
(a) $20$ K
(b) $4$ K
(c) $5$ K
(d) $12$ K
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Answer:
Correct Answer: 17. $(c)$
Solution:
$\Delta G=\Delta H-T \Delta S$
The process will be spontaneous, when
$ \Delta G=- \text { ve, i.e. }|T \Delta S|>|\Delta H| $
Given : $\Delta H=200 $ $J $ $mol^{-1}$ and $\Delta S=40 $ $JK^{-1}$ $ mol^{-1}$
$\Rightarrow \quad T>\frac{|\Delta H|}{|\Delta S|}=\frac{200}{40}=5 K$
So, the minimum temperature for spontaneity of the process is $5 K$.
BETA
