Gibbs-Duhem/Partial Molar Properties
Gibbs-Duhem Equation Useful for defining equilibrium concepts Integrate from state 1 to state 2 State 1: no mass (U,S,V,N)=0 State 2: some mass (U,S,V,N)<>0
Define U
Gibbs-Duhem Plug it in! When we are at equilbrium
Partial Molar Properties Consider equilibrium M(T,P,ni) M is any property (V, S, G, etc..) Partial molar property
Notation and Definition*** Look at derivative for definition M – extensive property m – intensive property To evaluate, just take the derivative
Terminology**** Example: mix 50 mL of water with 50 mL of ethanol, what happens? - Vi – V –
Derive contribution of partial molar properties
Derive contribution of partial molar properties
Simplifications System size can be anything System size can change by any amount Independent and arbitrary Both “brackets” are 0
Derive contribution of partial molar properties Gibbs-Duhem Eq
Derive for special case of binary system (from SVNA) Gibbs-Duhem Eq
Derive for special case of binary system (from SVNA)
Derive for special case of binary system (from SVNA)
Derive for special case of binary system (from Koretsky) Gibbs-Duhem Eq
Analytical Analysis From virial EOS, determine v1, v2, v, vIS, Δvmix, , and T=333 K P = 10 bar B11=-910 cc/mol B22=-1330 cc/mol B12=-2005 cc/mol y1=0.2
Analytical Analysis For v, just plug it in For v1 and v2, what should you do?
Analytical Analysis For v, just plug it in
Analytical analysis Ideal solution -
Analytical Analysis Binary system
Alternative Analytical Analysis If this WASN’T a binary system
Summary Gibbs-Duhem Defined partial molar properties Developed formula for binary mixtures Analytical solution Other than partial molar properties, plug and/or chug Remember formula for ideal solution
Summary For binary partial molar properties Convert all y2y1 (y2=1-y1) Take derivative Plug derivate and mixture property into formula simplify
Summary Partial molar properties (general) Convert from intensive to extensive Multiply by total moles Convert mole fractions to ni Take derivative Remember nT is a function of n1 n2 is NOT a function of n1 Simplify