Final answer:
The spontaneity of an exothermic process with a decrease in entropy mainly depends on the system's temperature, as described by the Gibbs free energy equation.
Step-by-step explanation:
The spontaneity of an exothermic process with a decrease in entropy depends primarily on the temperature of the system. This dependence is summarized by the Gibbs free energy equation ΔG = ΔH - TΔS, where ΔG is the change in free energy, ΔH is the change in enthalpy, and ΔS is the change in entropy.
It is noted that even if a process releases heat (exothermic), if there is a decrease in entropy, the process might not be spontaneous at low temperatures since the TΔS term might be too small to make ΔG negative. In contrast, at higher temperatures, the same process could become spontaneous if the TΔS term is large enough to outweigh a positive ΔH value, resulting in a negative ΔG, which is the condition for spontaneity.