Chemical Equilibrium

Equilibrium Chemical Physical Rates of the forward and reverse reactions are equal The concentrations of the reactants and products remain constant Between two phases of the same substance Changes that occur from physical processes N2O4 (g) 2NO2 (g) H2O (l) H2O (g)

Chemical Kinetics and Chemical Equilibrium ratef = kf [A][B]2 A + 2B AB2 kf kr rater = kr [AB2] Equilibrium ratef = rater kf [A][B]2 = kr [AB2] kf kr [AB2] [A][B]2 = Kc =

N2O4 (g) 2NO2 (g) equilibrium equilibrium equilibrium Start with NO2 Start with NO2 & N2O4

constant

N2O4 (g) 2NO2 (g) K = [NO2]2 [N2O4] = 4.63 x 10-3 aA + bB cC + dD K = [C]c[D]d [A]a[B]b

Equilibrium Will K = [C]c[D]d [A]a[B]b aA + bB cC + dD K >> 1 Lie to the right Favor products K << 1 Lie to the left Favor reactants

Equilibrium Homogeneous Heterogeneous Reactions in which all reacting species are in the same phase Reversible reaction involving reactants and products that are in different phases N2O4 (g) 2NO2 (g) Keq = [NO2]2 [N2O4] CaCO3 (s) CaO (s) + CO2 (g) Keq = [CO2] CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq) [CH3COO-][H3O+] [CH3COOH] Keq = The concentration of solids and pure liquids are not included in the expression for the equilibrium constant.

does not depend on the amount of CaCO3 or CaO CaCO3 (s) CaO (s) + CO2 (g) PCO 2 = Kp PCO 2 does not depend on the amount of CaCO3 or CaO

EXAMPLE At equilibrium and 100°C a flask contains: [PCl5]=0.0325M [H2O]=0.025M [HCl]=0.375M [POCl3]=0.250M Calculate the equilibrium constant for the reaction PCl5(g) + H20(g)  2HCl(g) + POCl3(g)