ABSTRACT
There is a very important theorem for cyclical processes which leads to the concept of entropy. This theorem is known as the Clausius inequality. This chapter shows how entropy changes are calculated, and determines the entropy change of a beaker of water when it is heated at atmospheric pressure between room temperature, at 20°C, and 100°C by placing it on a reservoir at 100°C. When the water reaches 100°C, the beaker is removed from the reservoir and placed in an insulating jacket. One simple reversible heating process between the end points could be affected by bringing up a whole series of reservoirs between 20°C and 100°C, keeping the pressure constant, so that the water passes through a series of equilibrium states.
