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**Unformatted text preview: **(nCGm,C + nDGm,D) – (nAGm,A + nBGm,B), and ∆rG° is similarly defined. ù, ú û 1 Now, at equilibrium, ∆rG = 0 and so, we get
n n é (P C /P ) C (P D /P ) D ù . , r G = −RT ln ê n n ú ë (P A /P ) A (P B /P ) B û eq The partial pressures that enter into this expression are the values measured at equilibrium and, therefore, is a constant at a given temperature. Note that, because of the division of each pressure term by the standard pressure, the quantity within the square brackets is dimensionless. In other words, , r G = −RT ln K , or P K = expé −, r G /(RT) ù . ë û P This is the thermodynamically correct definition of the equilibrium constant with respect to pressure. Note that, because of the division of each pressure term by the standard pressure, this is a dimensionless quantity. For real gases, the partial pressures must be replaced by the partial fugacities. The equilibrium constant can also be expressed in terms of concentrations by substituting PA = nART/V, etc.,...

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