Question

A reaction at 1 bar is non-spontaneous at low temperature but becomes spontaneous at high temperature. Identify the correct statement about the reaction among the following:

• A. both $\Delta H$ and $\Delta S$ are negative
• B. both $\Delta H$ and $\Delta S$ are positive
• C. $\Delta H$ is positive while $\Delta S$ is negative
• D. $\Delta H$ is negative while $\Delta S$ is positive

Answer 1

The correct option is B both $\Delta H$ and $\Delta S$ are positive

Both $\Delta H$ and $\Delta S$ are positive

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

At low temperature,

$T\Delta S<\Delta H$

$\Delta G>0$ and the reaction is non spontaneous.

At high temperature,

$T\Delta S>\Delta H$

$\Delta G<0$ and the reaction is spontaneous.