Question

Is an endothermic reaction with a decrease in entropy always spontaneous, never spontaneous or sometimes spontaneous and why

Answer 1

We know that Gibbs energy for a reaction is given by

Delta G = Delta H - T*Delta S...............(1)

Delta H is change in Enthalpy and Delta S is change in Entropy.

Since, reaction is endothermic, Delta H is positive.

Since entropy is decreasing, Delta S is negative.

Also, for spontaneous reaction, Delta G is always negative.

For non spontaneous reaction, Delta G is always positive.

It means the term Delta H is positive. ( endothermic reaction)

Term the term -T*Delta S is positive. ( Entropy decreasing thus Delta S is negative). So overall term -T*Delta S is +ve )

Since both the terms are positive, Delta G is positive.

And Delta G is positive, reaction will be non spontaneous.

Hence answer is reaction is non spontaneous.