Enthalpy of an Ideal Gas

The enthalpy change (H) of an ideal gas in a system is calculated by multiplying the number of moles of the gas (n), the constant pressure heat capacity (Cp), and the change in temperature (ΔT). Enthalpy is a state function and a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.

Heat capacity at constant pressure (Cp) is the amount of heat required to increase the temperature of the mass of the substance by one degree Celsius at constant pressure. The value of Cp is dependent on the particular gas and its conditions. The change in temperature (ΔT) must be in degrees Celsius or Kelvin, and it should be consistent with the units used for Cp. This formula assumes the ideal gas behavior, which is a good approximation for most gases under standard conditions.