A Graphical Representation: For the Fugacity of a Pure Substance


A graphical representation of the mathematical definitions that explains the relationship between fugacity and Gibbs energy for a pure substance has been discussed. The PG diagram shows that the solid/liquid and vapor/liquid coexistence curves would intersect at the triple point (83.8 K and 0.689 bars). The Gibbs energy of a substance behaving as an ideal gas can be determined at any temperature and pressure provided that the absolute (or standard) entropy of the ideal gas is known at some reference state. The residual Gibbs energy at constant pressure is the difference between the Gibbs energy of the system and the Gibbs energy of a system of the same chemical composition and at the same temperature and pressure but behaving as an ideal gas. The fugacity of a pure substance at a temperature and pressure is the pressure at which the substance behaving as an ideal gas at the same temperature has the same Gibbs energy as the system.


Chemical and Biochemical Engineering

Keywords and Phrases

Fugacity; Gibbs Energy; PG Diagram

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Document Type

Article - Journal

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© 2010 American Society for Engineering Education (ASEE), All rights reserved.

Publication Date

01 Aug 2010

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