Internal Energy

Internal energy of a system, is the energy content of the system due to its thermodynamic properties such as pressure and temperature. The change of internal energy of a system depends only on the initial and final states of the system and not in any way by the path or manner of the change. This concept is used to define the first law of thermodynamics.

Specific Internal Energy

Specific internal energy is defined as the internal energy of the system per unit mass of the system and naturally has the same dimension as [energy/mass] or enthalpy.