Question

For a certain process, and $\Delta H=178 \,kJ \Delta S=160\, J / K$. What is the minimum temperature at which the process is spontaneous (assuming that $\Delta H$ and $\Delta S$ do not vary with temperature)

• A. 2112.3 K
• B. 136.7 K
• C. 275.8 K
• D. 1112.5 K

Answer 1

Answer: (D)

According to Gibbs-Helmholtz reaction,
$\Delta G=\Delta H-T \Delta S$
For a spontaneous reaction, $\Delta G<0$
i.e., $\Delta H-T \Delta S<0$
or $T>\frac{\Delta H}{\Delta S}$
or $T>\frac{178 \times 1000}{160}$
$T>1112.5 \,K$
$\therefore $ For spontaneous process,
minimum temperature must be $1112.5 \,K$.