Unformatted text preview: the second-law relations for this system gives
dQ P dV dU dQ dS T dU P dV T ds 0 (162) Chapter 16
The differential of the Gibbs function (G ture and pressure is
1dG2 T,P dH 1dU dU T dS P dV P dV S dT V dP2 | 795 H TS) at constant tempera- G 0 T dS S dT 0
(163) dG < 0 dG = 0 dG > 0 T dS From Eqs. 162 and 163, we have (dG)T,P 0. Therefore, a chemical reaction at a specified temperature and pressure proceeds in the direction of a decreasing Gibbs function. The reaction stops and chemical equilibrium is established when the Gibbs function attains a minimum value (Fig. 164). Therefore, the criterion for chemical equilibrium can be expressed as
1dG2 T,P 0
(164) Violation of second law 100% reactants Equilibrium composition 100% products A chemical reaction at a specified temperature and pressure cannot proceed in the direction of the increasing Gibbs function since this will be a violation of the second law of thermodynamics. Notice that if the temperature or the pressure is changed, the reacting system will assume a different equilibrium state, which is the state of the minimum Gibbs function at the new temperature or pressure. To obtain a relation for chemical equilibrium in...
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This note was uploaded on 06/15/2009 for the course MAE 3311 taught by Professor Hajisheik during the Summer '08 term at UT Arlington.
- Summer '08