Question

For a given reaction, $△H=35.5kJmo{l}^{-1}$ and $△S=83.6J{K}^{-1}mo{l}^{-1}$. The reaction is spontaneous at: (Assume that $△H$ and $△S$ do not vary with temperature)

• A. $T>298K$
• B. $T<425K$
• C. $T>425K$
• D. All temperatures

Answer 1

Answer: (C)

$T>425K$

The reaction will be spontaneous when $\Delta G$ = negative

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

$\Delta H$ < $T\Delta S$

$T>\frac{\Delta H}{\Delta S}$

$T=\frac{35.5kJ/mol\times {10}^{3}J/kJ}{83.6J/K/mol}$

$T=425$
The reaction is spontaneous when $T>425K$