What does enthalpy (ΔH) represent?

Enthalpy, denoted as ΔH, represents the heat content of a system under conditions of constant pressure. It is a state function that reflects the total energy of the system minus the product of its pressure and volume. This concept is particularly important in thermodynamics because it allows for the measurement of heat exchange during chemical reactions and phase changes at constant pressure, which is a common condition in many practical scenarios.

When a reaction occurs at constant pressure, any heat absorbed or released by the system corresponds directly to a change in enthalpy. This is crucial in predicting and understanding the energy changes that accompany chemical processes. The use of enthalpy simplifies the calculations involved in these processes since it accounts for both internal energy changes and work done by or on the system under constant pressure conditions.

Other options refer to different thermodynamic concepts: total energy encompasses all forms of energy within the system, energy required to break bonds is specific to molecular interactions and does not directly represent ΔH without additional context, and change in temperature relates to thermal energy but does not specifically define enthalpy.