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| Phase Diagrams | ||||||||||||
| ·
For
systems in which the composition can change, the Gibbs
function must include a composition term so that: dG
= V dp - S dT + µ dN where
µ = (dG/dN)T.p = Chemical Potential · For the atom transfer between the phases, ( i, k) in thermodynamic equilibrium, the Gibbs function of each phase will change so that: ΔGi = (dGi / dNij) ΔNij and ΔGk = (dGk / dNkj ) ΔNkj · The system as a whole remains in equilibrium during this infinitesimal transfer consequently the total Gibbs function is constant: ΔGTotal = {ΔGi + ΔGk} = {µi - µk} ΔNkj = 0 · Since Nkj is not zero, equilibrium requires that: µi = µj · Two phases in thermodynamic equilibrium which are allowed to exchange atoms must have the same chemical potential. |
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