An Alternate Method of Introducing Fugacity

In current textbooks fugacity is introduced according to its differential or integral mathematical formulation. In this article an alternative method of explanation is offered. It is suggested that the real state of a pure gas can be described by comparing it to a hypothetical idealized state. The differences between these two states can then be expressed in terms of a function, Φ, defined as Φ(T,P) = μreal(T,P) - μideal(T,P) where μreal and μideal are the chemical potentials of the gas in its real and ideal states, respectively. The function Φ is a molar excess quantity and is expressed as Φ(T,P) = RTlnφ where φ is the fugacity coefficient. This approach introduces fugacity deductively through the Φ function, which leads to φ, the fugacity coefficient. This method is also appropriate for introducing the activity of solution components and the fugacity of a real gas in gaseous mixtures.