Question

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

Answer 1

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.

Answer 2

Answer:

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