Equilibrium Constant with respect to Partial Pressure (Kp)

For reactions involving gases, it is often more convenient to express the equilibrium constant in terms of equilibrium partial pressures rather than concentrations. For a general gaseous reversible reaction $aA(g)+bB(g)\rightleftharpoons cC(g)+dD(g)$, the equilibrium constant with respect to partial pressure, $K_p$, is defined as $K_p=\dfrac{P_C^{\,c}\,P_D^{\,d}}{P_A^{\,a}\,P_B^{\,b}}$, where $P_A$, $P_B$, $P_C$ and $P_D$ are the equilibrium partial pressures of A, B, C and D respectively. This is the pressure-based counterpart of $K_c$ (Section 12.4.3), and the two are related through the ideal gas equation, worked out in Sections 12.4.4 and 12.4.5. (Note: this sub-heading is printed with the same section number, '12.4.3', as the preceding $K_c$ subsection in the source tex …