Equilibrium [2]

Equilibrium [2] - Relationship of K to KP PC PD P P K = ref...

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1 6BH-Equilibrium (Basics) Keq Basics- 11 () –– (note that is dimensionless) cd CD ref ref ab AB ref ref abcd ref cdab P ref P ref PP K K K P KKP o r K K P + ++ = = ⎛⎞ ⎜⎟ ⎝⎠ == Relationship of K to K P 6BH-Equilibrium (Basics) Keq Basics- 12 [ ] [ ] ( ) [] [][] (note that is dimensionless as well) ref ref ref ref ref c ref c ref K Cc Dc K Ac Bc K c KK c o r K K c + = = Relationship of K to K c (or K eq )
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2 6BH-Equilibrium (Basics) Keq Basics- 13 Procedure for Mass Action Expression 1. Gases go into the expression in atm for the partial pressures of the gases involved; 2. Dissolved species enter the mass action expression as molar concentrations (M; mol/L); 3. Pure solids, liquids, and solvents* do NOT appear in an equilibrium expression (*provided solutions are dilute); 4. The final expression is Products/Reactants, with each raised to its balanced equation coefficient. This will give us K, the dimensionless thermodynamic equilibrium constant (assuming reference state is 1) 6BH-Equilibrium (Basics) Keq Basics- 14 Questions Raised • Why is the expression for K what it is? • Why does each reaction have a unique K? • What exactly determines this value? • Why does K change slightly over broad ranges of concentration (particularly high concentrations)? • Why is there a temperature dependence and what is it quantitatively? • How exactly does thermodynamics fit into the whole picture?
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3 6BH-Equilibrium (Basics) Keq Basics- 15 Thermodynamic Treatment of Equilibrium Consider the following reaction at non-reference conditions: We can model this using the following three reactions ( nr = non-reference ): 22 3 NO( ) N O( ) NO ( ) ? rxn gg g G ⎯⎯→ + ∆= ←⎯⎯ 1 2 22 2 2 3 ,, , , , 3 NO( ) 3 NO( ) 3 NO( N O( NO ( ) N O( NO ( ) N O( NO ( ) gn r gr e f e f e f e f e f e f r r G G G + ++ 6BH-Equilibrium (Basics) Keq Basics- 16 Thermodynamic Treatment of Equilibrium-2 For reaction 1: () 1 1 1 , 3 3 NO( 3 NO( ) 3l n n n l n n l n NO nr NO ref NO nr NO ref NO ref NO ref NO nr NO nr r e f G G G RT P RT P RT P P PP RT RT ⎛⎞ ⎜⎟ ⎝⎠ = = ==
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4 6BH-Equilibrium (Basics) Keq Basics- 17
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Equilibrium [2] - Relationship of K to KP PC PD P P K = ref...

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