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

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.