The First Law of Thermodynamics

The first law of thermodynamics formulates the conservation of energy for a thermodynamic system. Energy is introduced as the sum of kinetic, potential and internal—or thermal—energy. The energy of a closed system can only change due to energy transfer as work or heat. Internal energy is introduced as function of temperature and volume or pressure, and specific heats at constant volume and constant pressures are defined. Property relations for energy are presented for incompressible liquids and solids, and for ideal gases. Several reversible and irreversible processes are considered based on the first law, where it becomes clear that the first law alone does not suffice for the full description of irreversible processes.