Chemical Equilibrium 15
Chapter Overview
Equilibrium is defined and shown to be all around us every day. The chemical definition,
as well as “real world” references, are made. Appropriate calculations involved in equilibrium
Lecture Outline
15.1 Life: Controlled Disequilibrium
15.2 The Rate of a Chemical Reaction
Learning Objective: Identify and understand the relationship between concentration and
temperature and the rate of a chemical reaction.
15.3 The Idea of Dynamic Chemical Equilibrium
Learning Objective: Define dynamic equilibrium.
B. Rate of forward reaction the same as rate of reverse reaction
15.4 The Equilibrium Constant: A Measure of How Far a Reaction Goes
Learning Objective: Write equilibrium constant expressions for chemical reactions.
A. Not the same amount of stuff on each side of equation
15.5 Heterogeneous Equilibria: The Equilibrium Expression for Reactions Involving a Solid
or a Liquid
Learning Objective: Write equilibrium expressions for chemical reactions involving a
solid or a liquid.
15.6 Calculating and Using Equilibrium Constants
Learning Objective: Calculate equilibrium constants.
Learning Objective: Use the equilibrium constant to find the concentration of a reactant
15.7 Disturbing a Reaction at Equilibrium: Le Châtelier’s Principle
15.8 The Effect of Concentration Change on Equilibrium
Learning Objective: Apply Le Châtelier’s principle in the case of a change in
concentration.
15.9 The Effect of Volume Change on Equilibrium
15.10 The Effect of Temperature Change on Equilibrium
Learning Objective: Apply Le Châtelier’s principle in the case of a change in
temperature.
A. Exothermic: energy moves from system to surroundings
15.11 The Solubility-Product Constant
Learning Objective: Use Ksp to determine molar solubility.
15.12 The Path of a Reaction and the Effect of a Catalyst
Learning Objective: Describe the relationship between activation energy and reaction
rates and the role catalysts play in reactions.
Chemical Principle Teaching Ideas
Equilibrium
All chemical reactions are really equilibria, but many of them lie far to one side of the
Rates of Chemical Reactions
Some reactions, such as the rusting of metal, proceed very slowly. Some reactions such
Dynamic Chemical Equilibrium
Draw a basketball court on the board and draw nine X’s representing players on the
bench. What happens at the beginning of the game? Five people get up from the bench (react)
and get on to the court. This leaves four people on the bench. This represents the initial forward
Le Chatelier’s Principle
Most systems, when left to their own devices, reach a state of “happiness” where each
reactant has some fixed concentration. Left alone, they will stay “happy.” When you disturb the
Effect of Changes on Equilibrium
There are some changes that will not alter the equilibrium of a system. If the same
number of moles of gas are present on the reactant and product sides, then a shift in the V (or P)
will have no effect on the system.
Reaction Paths and Catalysts
The reaction pathway is sometimes referred to as the steps that a reaction goes through
Skill Builder Solutions
15.1. Because the coefficient in front of the HF(g) is a 2, the [HF] in the numerator must be
squared. The terms in the denominator are all single power as they both have a
coefficient of 1.
15.2. Water is a pure liquid, so it is not included in the equilibrium expression. The Cl2 has a
coefficient of 2, so [Cl2] must be squared in the expression. Likewise, the [HCl]
must be to the fourth power and the [O2] to the first, giving
Plus. The concentration of CO went down by 0.35 to 0.15, so [H2] went down by 0.35 × 2 =
0.70 to the equilibrium concentration is 1.00 – 0.70 = 0.30. For every 1 mole of CO that
15.6. The initial decrease in volume at constant temperature gives an increase in pressure
15.7. The reaction releases energy when proceeding to the right. To offset an increase in the
temperature of the system, the reaction will shift in the direction that absorbs energy,
Suggested Demonstrations
Carefully fill a syringe with NO2 gas from the reaction of HNO3 and Cu. In front of the students,
quickly adjust the volume of the syringe (with the syringe tightly capped). The color will change
suddenly and then adjust. This comes from the equilibrium between NO2 (brown) and N2O4
(colorless).
Guided Inquiry Ideas
Below are a few example questions that students answer in the guided inquiry activities provided
in the Guided Activity Workbook.
In a complete sentence, describe how the rate of a reaction depends on the concentrations of the
reactants?
In a complete sentence, describe how the rate of a reaction depends on the temperature.
Which factor seems to make a bigger difference in the rate: concentration or temperature?