Thermodynamics and Thermochemistry - Result Question 92
####17. Estimate the average $S-F$ bond energy in $SF _6$. The values of standard enthalpy of formation of $SF _6(g), S(g)$ and $F(g)$ are : $-1100,275$ and $80 kJ mol^{-1}$ respectively. (1999, 3M)
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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 : $\Delta H=200 Jmol^{-1}$ 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 $5 K$.
