Question

Under what conditions could some exothermic (ΔH<0) reactions be nonspontaneous (ΔG>0)?

Answer 1

Answer:

c. The overall reaction reduces entropy (products have less entropy than reactants).

Explanation:

The free energy change (delta G) for a reaction must have a negative value to allow the reaction to occur spontaneously. Free energy change depends on entropy (S) and enthalpy (H) of the reaction.

ΔG = ΔH  - T ΔS. If a reaction has positive enthalpy change and an overall increase in entropy, the reaction has negative free energy change and occurs spontaneously. However, if a reaction with positive enthalpy change has an overall reduction in entropy, the reaction will have a positive value of free energy change and cannot occur spontaneously.