Equilibrium
Ammonia
N2 + 3H2
2NH3
Ammonia
3H2(g) + N2(g)
2NH3(g)
N2O4(g)
2NO2(g)
N2O4(g)
2NO2(g)
Chemical Equilibrium
• reaction that proceeds forward (reactants
become products) and reverse (“products”
become “reactants”) at the same rate
• does NOT mean that amounts of reactants
and products are equal
Equilibrium Constant
• an expression and resulting numerical
value that describes the position of
equilibrium for a given reaction
Keq
Kc
Kp
Ksp
Ka
Kb
Equilibrium Constant
Kc = 1.9 x 1019
Equilibrium Constant
Kc = 4.1 x 10-31
Equilibrium Constant
K >> 1
equilib favors
products
K << 1
equilib favors
reactants
K≈1
equilib midway btw
Equilibrium Constant
aW + bX
cY + dZ
Kc = [Y]c[Z]d
[W]a[X]b
only solutions and gases appear in the
equilibrium constant expression, NOT
solids and pure liquids.
Equilibrium Constant
ClNO2(g) + NO(g)
NO2(g) + ClNO(g)
rateforward = ratereverse
kf[ClNO2][NO] = kr[NO2][ClNO]
k
[NO
][ClNO]
f
2
Keq = =
kr [ClNO2][NO]
Equilibrium Constant
Write the equilibrium constant expression for
the following reactions:
3H2(g) + N2(g)
CaCO3(s)
2NH3(g)
CaO(s) + CO2(g)
H2(g) + I2(g)
2HI(g)
Calculate a numerical value for Keq if the
equilibrium concentrations are
[H2] = 0.11 M
[I2] = 0.11 M
[HI] = 0.78 M
CH3CO2H(aq) + C2H5O(aq)
CH3CO2C2H5(aq) + OH-(aq)
At 25C, Kc = 4.10. In an equilibrium mixture, the
following concentrations were measured:
[CH3CO2H] = 0.210 M
[CH3CO2C2H5] = 0.910 M
[OH-] = 0.00850 M
What was the equilibrium concentration of ethanol?
Comparing Multiple Equilibria
• reversible reaction written in opposite
direction
½ N 2O 4
NO2
Kforward = [NO2]
[N2O4]1/2
Kforward = 0.11
NO2
½ N 2O 4
Kreverse =
Kreverse =
Comparing Multiple Equilibria
• reversible reaction written in opposite
direction
= equilibrium constant is inverted
Comparing Multiple Equilibria
• eqn that is a multiple of another equilib rxn
½ N 2O 4
N2O4
NO2
2NO2
Kc = [NO2]
[N2O4]1/2
Kc = 0.11
Kc’=
Kc’=
Comparing Multiple Equilibria
• eqn that is a multiple of another equilib rxn
= equilib constant raised to that factor
Comparing Multiple Equilibria
• equilib rxns added together to get an
overall reaction
A
2B
2B
3C
Kc
Kc
Comparing Multiple Equilibria
• equilib rxns added together to get an
overall reaction
= equilib constant of overall reaction is
the product of the individual equilib
constants
Do this without your calculator!
Given the following equilibrium reactions:
C2H2O4 ↔ H+ + C2HO4-
Kc= 6.5 x 10-2
C2HO4- ↔ H++ C2O42-
Kc= 6.1 x 10-5
Calculate Kc for the following reaction:
C2H2O4 ↔ 2H+ + C2O42-
Reaction Quotient
• Q
• written the same as an equilib constant,
but NOT at equilib conditions
Reaction Quotient
H2(g) + I2(g)
2HI(g)
[H2] = [I2] = 0.010M
[HI] = 0.050M
Kc = 60. (at 350oC)
Comparing Q and K
Q=K
rxn at equilb
Q<K
K>Q
proceeds toward
products
Q>K
K<Q
proceeds toward
reactants
PCl3 (g) + Cl2 (g)
PCl5 (g)
At a given temperature, the following
equilibrium concentrations were observed:
[PCl3] eq = 0.00300 M
[Cl2] eq = 0.00200 M
[PCl5] eq = 0.00670 M
Determine the value of the equilibrium
constant at this temperature.
At the same temperature, some Cl2(g),
PCl3(g), and PCl5(g) are mixed at the
following concentrations:
[Cl2] i = 0.0050 M
[PCl3] i = 0.063 M
[PCl5] i = 0.0038 M
In which direction will the reaction proceed
to achieve equilibrium?
ICE Tables
Initial (Concentrations)
Change
Equilibrium (Concentrations)