The following drawing is a representation of a reaction of the type A → B,where different shaded spheres represent different molecular structures.For this reaction ΔH° = -30 kJ.This reaction is likely to be
A)nonspontaneous at all temperatures.
B)nonspontaneous at low temperatures and spontaneous at high temperatures.
C)spontaneous at low temperatures and nonspontaneous at high temperatures.
D)spontaneous at all temperatures.

Question

The following drawing is a representation of a reaction of the type A → B,where different shaded spheres represent different molecular structures.For this reaction ΔH° = -30 kJ.This reaction is likely to be 
A)nonspontaneous at all temperatures. 
B)nonspontaneous at low temperatures and spontaneous at high temperatures. 
C)spontaneous at low temperatures and nonspontaneous at high temperatures. 
D)spontaneous at all temperatures.

Quizplus · Accepted Answer

The value of ΔH° is negative, indicating that the reaction is exothermic. However, the spontaneity of a reaction also depends on the entropy change (ΔS°). For a reaction of the type A → B, there is a decrease in the number of moles of gases and molecules, which leads to a decrease in the entropy of the system. 
As a result, the reaction will be spontaneous at low temperatures, where the negative enthalpy change dominates the positive entropy change, leading to a negative Gibbs free energy change (ΔG°) and a spontaneous reaction. However, at high temperatures, the positive entropy change dominates the negative enthalpy change, leading to a positive ΔG° and a non-spontaneous reaction. Therefore, the answer is C, spontaneous at low temperatures and non-spontaneous at high temperatures.

The Following Drawing Is a Representation of a Reaction of the Type