ABSTRACT
The first law of thermodynamics gives the precise relationship between the familiar concept of work and the new concepts of internal energy and heat. This chapter indicates that Joseph Black quantified heat using the method of mixtures. It explains how the first law justifies the idea of "heat lost equals heat gained". A set of simple relations for ideal gases can be obtained from the first law of thermodynamics. Some simple but important relations for ideal gases can be obtained by applying classical mechanics to the motion of individual molecules in a gas. This approach is called kinetic theory and is valid because it deals with mean values of molecular energy without going into specifics about the statistical distribution of energy. The chapter concludes with a brief discussion of steady flow processes, which are of particular importance in engineering.
