Phase changes Liquid-Vapor Equilibrium liquid gas evaporation gas liquidcondensation depends on T depends on [vapor]

vapor pressure = 1 atmboiling point

Equilibrium A + B  C C rate =kfkf [A][A][B][B] C  A+ B rate = krkr [C] k f [A][B] = k r [C] kfkf krkr = [C] [A] [B] = K equilibrium constant

Law of Mass Action aA+ bB cC + dD K =[C] c [D] d [A] a [B] b  O3O3  O2O2 23at 2300 o CK = 2.5 x = [O 2 ] 3 [O 3 ] 2 if [O 2 ] = 0.50 Mat equilibrium 2.5 x = (0.50) 3 [O 3 ] 2 [O 3 ] = 2.2 x M

aA+ bB cC + dD K =[C] c [D] d [A] a [B] b  O3O3  O2O2 23at 2300 o CK = 2.5 x = [O 2 ] 3 [O 3 ] 2 Law of Mass Action O2O2  O3O3 32 K = = [O 3 ] 2 [O 2 ] x K = 4 x large K  small K  excess product excess reactant

Law of Mass Action CO (g) + H 2 O (g)  H 2 (g) +CO 2 (g) at 830 o C equilibrium concentrations [CO] = 0.20 M [H 2 O] = 0.40 M [H 2 ] = 0.30 M [CO 2 ] = 1.36 M K = (0.30)(1.36) (0.20)(0.40) = 5.10 homogeneous equilibriumall in one phase gas K = M (mol/L) gasesP PV=nRT n V = P RT K P = Δn = mol gas reactants K(RT) ΔnΔn mol gas product - K P = K

K(RT) ΔnΔn 2 NO (g)+ O 2 (g)  2NO 2 (g) at 230 o C equilibrium concentrations [NO] = M [O 2 ] = M [NO 2 ] = 15.5 M K = (0.0542) 2 (0.127) = 6.44 x 10 5 K P = 6.44 x 10 5 ( )(503 K) = 1.56 x 10 4 K and K P are dimensionless no units (15.5) 2

Heterogeneous Equilibria s, l, g CaCO 3 (s)  CaO (s) +CO 2 (g) 3 phases K = [CO 2 ] [CaO] [CaCO 3 ] [CaO]mol L = density L g ÷ M.W. g mol constants solids don’t appear in K = [CO 2 ] pure liquids don’t appear H 2 O as a solvent

Predicting the direction of a reaction  2 HI (g) H 2 (g)+ I 2 (g) at 430 o CK = 54.3 start with:0.243 mol H mol I mol HI 1.0 L flask [HI] 2 0 [H 2 ] 0 [I 2 ] 0 0 = initial = (0.243)(0.146) =  54.3 not at equilibrium too much product reverse reaction

Reaction Quotient, Q Q = [products] 0 [reactants] 0 K = [products] eq [reactants] eq Q > K reverse Q = Ksystem at equilibrium Q < K forward reaction proceeds

Reaction Quotient, Q N 2 (g) + 3H 2 (g)  2 NH 3 (g) at 200 o C, K = 0.65 [N 2 ] 0 = M [H 2 ] 0 = 9.17 x M [NH 3 ] 0 = 1.83 x M Q =(1.83 x ) 2 (9.17 x ) 3 (0.0711) = reaction proceedsforward

Mg(OH) 2 (s) Mg OH -  K = [OH - ] eq [Mg 2+ ] eq add H + reacts with OH - Q K > < Q = [OH - ] 0 [Mg 2+ ] 0 reaction proceeds forward