3 Equilibrium constant Kc

For a generalised reaction mA + nB pC + qD m,n,p,q are the stoichiometric balancing numbers A,B,C,D stand for the chemical formula Equilibrium constant Kc [ C]p [D]q [ A]m [B]n Kc= [ ] means the equilibrium concentration Kc = equilibrium constant Example 1 N2 (g) + 3H2 (g) 2 NH3 (g) [NH3 (g)] 2 [N2 (g)] [H2 (g)] 3 Kc= Calculating Kc In a container of volume 600cm3 at equilibrium the concentrations of the substances were 0.67 mol dm-3 of H2 and 0.83 mol dm-3 of Cl2 and 0.33 mol dm-3 HCl. Calculate Kc H2 (g) +Cl2 (g) 2HCl (g) Example For the following equilibrium = 0.332 0.67×0.83 Kc = 0.196 no unit Kc= [HCl (g)] 2 [H2 (g) ] [Cl2 (g)] N Goalby chemrevise.org 3 The larger the Kc the greater the amount of products. If Kc is small we say the equilibrium favours the reactants Kc only changes with temperature. It does not change if pressure or concentration is altered. A catalyst also has no effect on Kc