Chapter 4: The First Law of Thermodynamics

In the preceding chapter we categorized all energy interactions between a system and its surroundings either as work or heat. This was a useful starting-point for the introduction of the First Law of Thermodynamics, which is essentially the law of conservation of energy formulated in a unified manner to include all energy forms. The first law relates work and heat interactions that occur at the boundary of a system, to the energy possessed or stored by a system, which we shall call the internal energy of the system. The emphasis in this chapter will be the application of the first law to a closed system undergoing steady processes. In the next chapter we shall consider open systems and transient or unsteady processes.