Question

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

a. The products have greater potential energy than the reactants.
b. The products and reactants have equal entropy.
c. The overall reaction reduces entropy (products have less entropy than reactants).
d. The overall reaction results in an increase in entropy (products have greater entropy than reactants)

Answer 1

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

Step-by-step 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.