CHEMICAL EQUILIBRIUM
Ch. 16
There are seven main ideas in this chapter.
1.
Reversible Reactions
2.
The Mass Action Expression, which at equilibrium equals the equilibrium
constant, K.
3.
Manipulating K to increase its utility.
4.
The Mass Action Expression not at equilibrium, which equals the reaction
quotient, Q.
5.
Factors that affect an equilibrium (and how).
6.
Calculating values for K and for equilibrium concentrations of reactants or
products.
7.
Equilibrium and Thermodynamics (deferred until after Ch. 14).
1.
Reversible Reactions Sec. 16.1
Irreversible Reactions
Reversible Reactions
1
Book Example: Water-Gas shift Reaction: reaction of CO(g) with steam.
CO(g) + H2O(g)
H2(g) + CO2(g)
2.
The Mass Action Expression (MAE). Sec. 16.2
At equilibrium it equals the equilibrium constant, K.
For:
aA + bB
MAE equals:
Kc equals:
dD + eE
Kc for the water-gas reaction:
Kp for the water gas reaction:
2
2a. Numerical Values of Kc & Kp.
Need concentrations or partial pressures.
2b. Kc and Kp are qualitatively related. Sec. 16.3
3
2c. Meaning of Kc, Kp
3.
Manipulating K to increase its utility. Sec. 16.4
3a. Reversing a Reaction
K for the forward reaction
K for the reverse reaction
3b. Multiplying an equation by a number.
3c. Summing Reactions
4
4.
The Mass Action Expression not at equilibrium, which equals the reaction
quotient, Q. Sec. 16.5
5
4a. Homogeneous and Heterogeneous Equilbria have different MAE (Sec. 16.6)
5.
Factors that affect an equilibrium (and how). Le Chatelier’s Principle
Sec. 16.7
If a system at equilibrium is perturbed it will react in such a way as to re-establish the
equilibrium. Perturbations include adding/subtracting reaction components; changing
pressure (gas-phase reactions only); and changing temperature.
5a. Changing concentrations of reaction components
6
5b. Changing internal pressure in gas-phase reactions.
5c. Changing temperature.
5d. Catalysts have no effect on a chemical equilibrium. Catalysts only affect reaction
kinetics and we will return to catalysts in Ch. 14.
6.
Calculating values for K and for equilibrium concentrations of reactants or
products. Sec. 16.8
ICE Tables.
I = initial reactant and product concentrations;
C = how the concentrations of reactants and products change as the reaction proceeds
according to the balanced equation;
E = Concentrations of reactants and products once the reaction has reached
equilibrium
Calculate the missing values for each set of data
in the table.
7
8
9
Section 16.9 and 16.10 are deferred until the Thermodynamics Chapter.
End Ch. 16 notes.
10