Question

When are reactions always spontaneous?

A) when the reaction is endothermic and the entropy is decreasing at a low temperature
B) when the reaction is exothermic and the entropy is increasing at a high temperature
C) when the reaction is endothermic and the entropy is increasing at a high temperature
D) when the reaction is exothermic and the entropy is decreasing at a low temperature

Answer 1

A spontaneous process is the time-evolution of a system in which it releases free energy and moves to a lower, more thermodynamically stable energy state.12The sign convention of changes in free energy follows the general convention for thermodynamic measurements, in which a release of free energy from the system corresponds to a negative change in free energy, but a positive change for the surroundings.

Answer 2

B) when the reaction is exothermic and the entropy is increasing at a high temperature

Step-by-step explanation:

Spontaneity of a chemical reaction is given by the Gibb’s free energy equation:

ΔG = ΔH – TΔS

For a spontaneous reaction ΔG is negative. For ΔG to be negative ΔH must be negative or when the reaction is exothermic. Also for ΔG to be negative ΔS must be positive or increase at higher temperature such that the magnitude of |TΔS| is high. Combination of negative ΔH and positive ΔS at high T will make ΔG negative, and thus the reaction spontaneous.