Question

A particular reaction is spontaneous upto 475k and becomes non-spontaneous at temperatures above 475k. (i) is this reaction exothermic or endothermic?

Answer 1

Answer : This reaction is exothermic reaction.

Explanation :

According to Gibbs's equation:

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

$\Delta G$ = Gibbs free energy  

$\Delta H$ = enthalpy change

$\Delta S$ = entropy change  

T = temperature in Kelvin

When $\Delta G$ is positive then the reaction is non spontaneous.

When $\Delta G$ is negative then the reaction is spontaneous.

When $\Delta G$ is equal to 0 then the reaction is in equilibrium.

As per question,

At low temperature (upto 475 K) and at high temperature (above 475 K), the reaction is spontaneous and non-spontaneous respectively, that means the value of $\Delta H$ = -ve and the value of $\Delta S$ = -ve.

When the value of $\Delta H$ = -ve and the value of $\Delta S$ = -ve then the reaction will be exothermic.

Hence, the reaction is exothermic reaction.