Equilibrium Constants 201 Chemistry

Equilibrium: Crash Course Chemistry #28

Kc is a constant at a certain temperature Equilibrium constant Each equilibrium reaction has an equilibrium constant Kc. aA + bB ↔ cC + dD Kc is a constant at a certain temperature Kc = products [C]c x [D]d reactants [A]a x [B]b [] = concentration Page 6

Write the equilibrium expression from the following a) 2NH3(g) ↔ N2(g) + 3H2(g) b) 2N2(g) + 6H2(g) ↔ 4NH3(g) c) CH3COOH(aq) + H2O(l) ↔ CH3COO (aq) + H3O +(aq) Page 6

Equilibrium Constants Indicates the extent to which the equilibrium favours products or reactants.   If Kc is very large (>>1 e.g. 1x 106) then at equilibrium there will be far more products than reactants. H2(g) + Cl2(g) ↔ 2HCl(g) Kc = 4.0 x 1031 at 300 oC This indicates that at equilibrium there is virtually no H2 and Cl2 present. Page 6 & 7

Equilibrium Constants  If Kc is very small (<<1 e.g. 1x 10-6) then there are far more reactants than products. CH3COOH(aq) + H2O(l) ↔ CH3COO(aq) + H3O+(aq) Kc = 1.8 x 10-5 at 25 oC   Very few of the ethanoic acid molecules split up into hydrogen and ethanoate ions. Page ???

Calculations of Kc A mixture of hydrogen and iodine was heated in a sealed flask at 491oC and, at equilibrium, the concentration of hydrogen was 2.5 x 10-2 mol L-1, iodine was 2.5 x 10-2 mol L-1, and hydrogen iodide was 1.71 x10-1 mol L-1. Calculate Kc. H2(g) + I2(g) ↔ 2HI(g) Kc = [HI]2 = (1.71 x 10-1)2 = 46.8 [H2][I2] (2.5 x 10-2) x (2.5 x 10-2)