What does the term "enthalpy change" (ΔH) refer to in chemistry?

The term "enthalpy change" (ΔH) refers specifically to the heat content change that occurs during a chemical reaction at constant pressure. Enthalpy is a thermodynamic property that combines internal energy with the product of pressure and volume (H = U + PV). When a reaction takes place under constant pressure, the change in enthalpy reflects the heat energy absorbed or released during the process.

This concept is essential in understanding how reactions either absorb heat (endothermic reactions, where ΔH is positive) or release heat (exothermic reactions, where ΔH is negative). Essentially, ΔH provides insight into the energy dynamics of chemical reactions, making it a fundamental concept in thermochemistry.