Therefore, the internal energy is a state function. The variables q and w lack that uniformity. It is found that the same quantity of work must be done on an adiabatic system to achieve the same change of state even though different means of achieving that work may be used. In each case, the change in enthalpy depends on the heat capacities of the substances. The work done during the irreversible expansion against the same final pressure is the rectangular area.
Reversible work is greater than irreversible work.