Enthalpy (H = U + PV) is a state function that, under constant-pressure conditions, equals the heat added to a system, providing a practical way to quantify energy changes in chemical reactions. The standard heat of formation (ΔH°f) is the change in enthalpy when a compound is formed from its constituent elements in their standard elemental states at standard temperature and pressure, and its sign determines whether a reaction is exothermic (negative ΔH, heat released, product more stable/lower potential energy) or endothermic (positive ΔH, heat absorbed). This concept belongs to thermochemistry, a branch of physical chemistry, and provides the foundational framework, via tabulated formation values, for predicting the heat released or absorbed by chemical reactions relative to a defined elemental reference state.
Enthalpy (H = U + PV) is a state function that, under constant-pressure conditions, equals the heat added to a system, providing a practical way to quantify energy changes in chemical reactions. The …