ABSTRACT
The transfer of work and/or heat to a system from the environment causes a change in the state of the system. The first law expresses the conservation of energy and equates the change in internal energy of the system as equal to the difference between the heat transfer to the system and the work done by the system on the environment. The increase of internal energy of a system is from the dissipative mechanical work done on the system in the absence of heat transfer or from the heat transfer to the system. The sum of work and heat transfer in a cyclic process is equal and provides the equivalence of heat transfer and work. Heat transfer, like work, is path-dependent and gives rise to two different values of heat capacities at constant volume and constant pressure. The generalized relations between the two heat capacities are determined and their values for ideal gas are inferred. Internal energy changes from temperature and pressure changes and enthalpy changes from temperature and volume changes are determined. In the case of an ideal gas, the change of internal energy and enthalpy depends only on change of temperature. The Joule coefficient and the Joule Thomson coefficient that relate the variation of temperature due to expansion at constant values of internal energy and enthalpy, respectively, are discussed. The first law is also applied to an open system.
