Heterogeneous Equilibria
1. What is meant by the following?
a) Homogeneous Equilibrium
b) Heterogeneous Equilibrium
2. Dddd
The concentrations of pure solids, pure liquids, and solvents are omitted from equilibrium
constant expressions because they do not change significantly during reactions when enough
is present to reach equilibrium.
3. jjj
Write each expression for KK, incorporating all constants, and KpKp for the following
equilibrium reactions.
a. PCl3(l)+Cl2(g)⇌PCl5(s)PCl3(l)+Cl2(g)⇌PCl5(s)
b. Fe3O4(s)+4H2(g)⇌3Fe(s)+4H2O(g)Fe3O4(s)+4H2(g)⇌3Fe(s)+4H2O(g)
Given: balanced equilibrium equations
Asked for: expressions for KK and KpKp
Strategy:
Find KK by writing each equilibrium constant expression as the ratio of the concentrations of the
products and reactants, each raised to its coefficient in the chemical equation. Then
express KpKp as the ratio of the partial pressures of the products and reactants, each also raised to
its coefficient in the chemical equation.
Solution:
This reaction contains a pure solid (PCl5PCl5) and a pure liquid (PCl3PCl3). Their concentrations
do not appear in the equilibrium constant expression because they do not change significantly. So
K=1[Cl2]K=1[Cl2]
and
Kp=1PCl2Kp=1PCl2
This reaction contains two pure solids (Fe3O4Fe3O4 and FeFe), which do not appear in the
equilibrium constant expressions. The two gases do, however, appear in the expressions:
K=[H2O]4[H2]4K=[H2O]4[H2]4
and
Kp=(PH2O)4(PH2)4