Energy balance equation for the closed system

As a mathematical interpretation on the first law, we can formulate the conservation of energy concept into equations, called energy balance equation.

The first and the most simple formulation is for the closed system, where there is no material exchange with surroundings. In energy balance equation for the closed system, the energy change of the system is described as the energy change of internal energy, potential energy and the kinetic energy. For energies in transit (the energies transferring between system and surrounding), only two types of energies are involved: the heat and work.