Solutions and Equilibrium

Heterogeneous Equilibrium• Reaction occurs in more than one phase• KEQ = Products

Reactants• Solids and liquids are not included in the

equilibrium constant expression for heterogeneous equilibrium

FeO(s) + CO(g) Fe(s) + CO⇌ 2(g)

KEQ = [CO2]

[CO]

The concentration of pure solid or liquid is not included in the equilibrium constant expression

for heterogeneous equilibrium.

Solubility Product Constant• The equilibrium constant for the solubility

equilibrium of a slightly soluble ionic compound

BaSO4(s) Ba2+(aq) + SO42-(aq)

Ksp = [Ba2+] [SO42- ]

PbI2 Pb2+(aq) + 2I-(aq)

Ksp = [Pb2+] [I-]2

Solubility Product Constant

** If Ksp is small = low solubility

BaSO4 Ksp = 1.1 X 10-10

CaSO4 Ksp = 2.4 X 10-5

Fe(OH)2 Ksp = 7.9 X 10-16

Which is most soluble?CaSO4

Which is least soluble? Fe(OH)2

Common Ion Effect• When a common ion reduces the solubility

of a salt

What is the common ion?Cl-

Which direction is equilibrium driven?Left – forming more undissolved NaCl

Learning Check

• If KBr is added to a solution containing PbBr2(aq), will more PbBr2 solidify?

• Yes

• If KBr is added to a solution containing NaCl, will more NaCl precipitate? • No, no common ion

Reactions that go to Completion• KEQ is large

• A gas leaves the system

2KClO3(s) 2KCl(s) + 3O2(g)

• Water is formed

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

• A precipitate is made (Table F)

AgNO3(aq) + NaCl(aq)

NaNO3(aq) + AgCl(s)