How does enthalpy affect the spontaneity of a reaction?

Enthalpy, represented as ΔH, plays a crucial role in determining the spontaneity of a reaction through its influence on the Gibbs free energy change (ΔG). A reaction is spontaneous if ΔG is negative, which can occur when the enthalpy change is favorable (exothermic, ΔH < 0) or when the entropy change (ΔS) is favorable enough to offset an unfavorable ΔH. However, if a reaction is endothermic (ΔH > 0), it may still be spontaneous at higher temperatures if the increase in entropy (ΔS > 0) is significant enough to result in a negative ΔG. Thus, both enthalpy and entropy must be considered together to assess spontaneity.