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**Unformatted text preview: **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 = exp é −, 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., and recognizing that nA/V = [A], etc., to get
n C +n D −n A −n B
K = K C æ RT ö
, where
P
è P ø KC = [C ] n C [D ] n D
.
[A ] n A [B ] n B Also, by recalling that PA = xAP, where xA is the mole fraction of A and P is the
total pressure at equilibrium, we ca...

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