Question

$\Delta H$ and $\Delta S$ for a reaction are $+30.558kJ{mol}^{-1}$ and $0.066kJ{K}^{-1}{mol}^{-1}$ at $1$atm pressure. The temperature at which free energy change is zero and the nature of the reaction below this temperature is:

• A. $483K$,spontaneous
• B. $443K$ non-spontaneous
• C. $443K$,spontaneous
• D. $463K$ non-spontaneous
• E. $463K$,spontaneous

Answer 1

The correct option is D $463K$ non-spontaneous

$\Delta H=+30.558KJ/mol$

$\Delta S=0.066KJ/mol$

$P=1atm$

$\Delta G=\Delta H-T\Delta S$

$O=30.558-0.066\times T$

$\therefore T=\frac{30.558}{0.066}$

$\therefore T=463K\Rightarrow △G=0$

As temperature decreases, the $T\Delta S$ term decreases and as $\Delta H$ is positive, the $\Delta G$ terms becomes greater than zero which means that reaction becomes non-spntaneous.