The entropy of an exothermic reaction decreases. This reaction will be spontaneous under which of the following temperatures?

a) High temperatures

b) Low temperatures

c) All temperatures

d) No temperatures

Answer:Low temperatures

Explanation:

∆G = ∆H-T∆S

If ∆H is negative (exothermic reaction), then in order to maintain ∆G<0 which is the condition for spontaneity; T must decrease. This is because, decrease in T will keep the difference of ∆H and T∆S at a negative value in order to satisfy the above stated condition for spontaneity.

B - Low Temperatures

Explanation:

For a reaction to be spontaneous, the Gibb's free energy value has to be negative and to achieve this: the enthalpy, entropy and temperature have to meet certain criteria.

ΔG=ΔH-TΔS

• When the enthalpy is below 0 and entropy is above 0, the reaction

spontaneous

• When the enthalpy is below 0 and the entropy is above zero, the

reaction is spontaneous only at high temperatures

• When the enthalpy and entropy is below 0, the reaction can be

spontaneous only at low temperatures

• When both the enthalpy is above 0 and entropy below 0, the

reaction cannot be spontaneous

From the above explanation, we can infer that a decrease in entropy will require a low temperature and a low enthalpy for the reaction to be spontaneous