1. Chemical Equilibrium

2. 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)

3. 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 =

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

5. constant

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

7. 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

8. 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) NO2 (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.

9. 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

10. 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)