ABSTRACT
The concept of temperature is fundamental to any study of thermodynamics. Much of thermodynamics concerns the changes that occur to both systems when one or more of these three kinds of equilibrium, namely mechanical equilibrium, chemical equilibrium and diffusive equilibrium do not exist. The important point is that state variables and thermodynamic variables are required to specify the equilibrium state of a simple system. The method of setting the temperature scale was changed in 1954 from a two-point method to the current single-point method. For convenience, it would be desirable to have a temperature scale in which the zero is in the range of commonly encountered temperatures. The ideal gas scale can equally be defined using constant-pressure thermometers rather than constant-volume thermometers. This chapter explains the limitations of the thermodynamic scale. The temperature of a system determines whether or not that system is in thermal equilibrium with other systems.
