NotesFAQContact Us
Search Tips
Peer reviewed Peer reviewed
Direct linkDirect link
ERIC Number: EJ820294
Record Type: Journal
Publication Date: 2006-Jul
Pages: 4
Abstractor: As Provided
Reference Count: 16
ISSN: ISSN-0021-9584
Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction
Tellinghuisen, Joel
Journal of Chemical Education, v83 n7 p1090-1093 Jul 2006
Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V, the Helmholtz energy A seeks a minimum. These points are illustrated for the ammonia formation reaction in the ideal gas approximation, through a numerical exercise in which both G and A are evaluated as functions of the extent of reaction [xi], under conditions of constant (T,P) and constant (T,V), for the same starting thermodynamic state. The equilibrium positions are different, but at both minima--in G[subscript T,P]([xi]) and A[subscript T,V]([xi])--the value of the reaction quotient Q equals the equilibrium constant K[degree](T). In the familiar thermodynamics equation defining K[degree], RT ln K[degree] = -[delta]G[degree] [delta]G[degree] has its origin in the fact that the chemical potential for a pure substance is its molar Gibbs energy, rather than from considerations about the conditions under which equilibrium occurs. (Contains 2 figures and 5 notes.)
Division of Chemical Education of the American Chemical Society. Subscription Department, P.O. Box 1267, Bellmawr, NJ 08099-1267. Tel: 800-691-9846; Tel: 856-931-5825; Fax: 856-931-4115; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education; Postsecondary Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A