lec2_2011 - Review: Expressions of the thermodynamic...

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Review: Expressions of the thermodynamic equilibrium constant K K , (a dimensionless quantity) can be expressed in terms of fugacities for gas phase reactions or activities for aqueous phase reactions. Gas phase: Fugacity ( a dimensionless quantity) is equal to the numerical value of partial pressure, i.e. p j /p θ where p θ = 1 bar). Aqueous phase: 1. Neutral solution: the activity, a , is equal to the numerical value of the molality, i.e. b j /b θ where b θ = 1 mol kg -1 . 2. Electrolyte solution: The activity shall now be calculated as α j = γ j *b j /b θ , where the activity coefficient, γ, denotes distance from the ideal system where there is no ion-interactions among constituents.
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The activities of solids and pure liquid are equal to 1 α (solid) = 1 and α (pure liquid) = 1 (!!!) Illustration: Express the equilibrium constant for the heterogeneous reaction NH 4 Cl(s) ↔ NH 3 (g) + HCl(g) Solution: In term of fugacity (i.e. thermodynamic equilibrium constant): K p = In term of molar fraction: K x =
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Estimate reaction compositions at equilibrium Example 1: Given the standard Gibbs energy of reaction H 2 O(g) → H 2 (g) + 1/2O 2 (g) at 2000K is + 135.2 kJ mol -1 , suppose that steam at 200k pa is passed through a furnace tube at that temperature. Calculate the mole fraction of O 2 present in the output gas stream.
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lec2_2011 - Review: Expressions of the thermodynamic...

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