# 25.7: Partial Pressure of Reacting Gas

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Using equations (15) we can see that the equilibrium constant is related to the partial pressures of reacting gases:

$K_p = \frac{p_C}{p_Ap_B}$

for the reaction

$A + B \rightarrow C$

(Remember that these pressures must be related to a standard state.)

For a metal oxidation reaction

2M (s) + O2 (g) = 2MO (s) ,

the equilibrium constant has the form

$K_p = \frac{1}{p_{O_2}}$

$p_{O_2}|_{eq.,T} = exp( \frac{\Delta G^{\circ}}{RT} )$