This preview shows page 1. Sign up to view the full content.
Unformatted text preview: gf dmf gg dmg since gf and gg remain constant at constant temperature and pressure. At dmf. equilibrium, (dG)T,P 0. Also from the conservation of mass, dmg Substituting, we obtain
1dG2 T,P 1gf gg 2 dmf which must be equal to zero at equilibrium. It yields
(1619) Therefore, the two phases of a pure substance are in equilibrium when each phase has the same value of specific Gibbs function. Also, at the triple point (the state at which all three phases coexist in equilibrium), the specific Gibbs functions of all three phases are equal to each other. Chapter 16
What happens if gf gg? Obviously the two phases are not in equilibrium at that moment. The second law requires that (dG)T, P (gf gg) dmf 0. Thus, dmf must be negative, which means that some liquid must vaporize gg. Therefore, the Gibbs function difference is the driving force until gf for phase change, just as the temperature difference is the driving force for heat transfer. | 809 EXAMPLE 167 Phase Equilibrium for a Saturated Mixture Show th...
View Full Document
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