For a weak electrolyte generalizing as with a " molar" initial concentration and a degree of dissoci — Ionic Equilibrium Chemistry Question
Question
For a weak electrolyte generalizing as $A_xB_y$ with a "$c$ molar" initial concentration and a degree of dissociation $\alpha$, which of the following expressions precisely defines its equilibrium constant $K_{eq}$?
💡 Solution & Explanation
The dissociation reaction is $A_xB_y \rightleftharpoons xA^{y+} + yB^{x-}$. Initially, $[A_xB_y] = c$. At equilibrium, $[A_xB_y] = c(1-\alpha)$, $[A^{y+}] = xc\alpha$, and $[B^{x-}] = yc\alpha$. The equilibrium constant is $K_{eq} = \frac{[A^{y+}]^x[B^{x-}]^y}{[A_xB_y]} = \frac{(xc\alpha)^x(yc\alpha)^y}{c(1-\alpha)} = \frac{x^x y^y c^{x+y} \alpha^{x+y}}{c(1-\alpha)} = \frac{x^x y^y c^{x+y-1} \alpha^{x+y}}{1-\alpha}$.