Question

A change in the free energy of a system at constant temperature and pressure will be:
${\Delta }_{sys}G={\Delta }_{sys}H-T{\Delta }_{sys}S$
At constant temperature and pressure,
${\Delta }_{sys}G<0\left(spontaneous\right)$
${\Delta }_{sys}G=0\left(equilibrium\right)$
${\Delta }_{sys}G>0(non-spontaneous)$

A reaction has positive values of $\Delta H$ and $\Delta S$.

From this you can deduce that the reaction:

• A. must be spontaneous at any temperature
• B. cannot be spontaneous at any temperature
• C. will be spontaneous only at low temperature
• D. will be spontaneous only at high temperature

Answer 1

The correct option is D will be spontaneous only at high temperature

As we know,
$\Delta G=\Delta H-T\Delta S$ and for a spontaneous reaction,

$\Delta G=-ve$

This happens only at higher temperatures.

Therefore, D option is right.