Distinguish exothermic and endothermic reactions using enthalpy change signs.

Exothermic reactions release energy to the surroundings, resulting in a decrease in enthalpy, indicated by a negative enthalpy change (ΔH < 0). Common examples include combustion and respiration. In contrast, endothermic reactions absorb energy, leading to an increase in enthalpy, represented by a positive enthalpy change (ΔH > 0). Photosynthesis is a typical endothermic process. The key difference lies in energy transfer: exothermic reactions release energy, while endothermic reactions require energy input. Understanding these distinctions is crucial for predicting reaction behavior and energy changes in chemical processes.