Enthalpy is a thermodynamic property defined as the sum of a system's internal energy and the product of its pressure and volume. Mathematically, it is expressed as:
H=U+PVH=U+PVH=U+PV
where HHH is enthalpy, UUU is internal energy, PPP is pressure, and VVV is volume
. Enthalpy is a state function, meaning it depends only on the current state of the system (temperature, pressure, and internal energy) and not on how the system reached that state
. It is an extensive property, proportional to the size of the system, but can be expressed in specific or molar terms for convenience
. In practical terms, enthalpy accounts for the energy required to create the system (internal energy) plus the energy needed to make room for it by displacing the surroundings at constant pressure (the PVPVPV work)
. This makes enthalpy particularly useful in chemistry and physics when dealing with processes at constant pressure, such as many chemical reactions occurring in the atmosphere. The change in enthalpy (ΔH\Delta HΔH) during a process at constant pressure equals the heat absorbed or released by the system:
ΔH=ΔU+PΔV\Delta H=\Delta U+P\Delta VΔH=ΔU+PΔV
This relationship allows enthalpy to serve as a measure of heat flow in chemical and physical processes
. In summary, enthalpy represents the total heat content of a system, combining internal energy and the energy associated with pressure-volume work, making it a fundamental concept in thermodynamics for understanding energy changes in various systems
