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.

That result from subduction of oceanic plates beneath lighter continental plates. most of the earth's volcanoes are located around the pacific ring of fire because that the location of most of the earth's subduction zones.