Chapter 16

Essential Question: What are the characteristics of chemical equilibrium? How are equilibrium expressions written for systems that are at equilibrium? How are equilibrium constants calculated from concentration data?
Vocabulary:
- Reversible reaction
- Chemical equilibrium
- Law of chemical equilibrium
- Equilibrium constant
- Homogeneous equilibrium
- Heterogeneous equilibrium
Chemical Equilibrium: A state where forward and reverse reactions balance, occurring at equal rates (Rateforward reaction = Ratereverse reaction).
Law of Chemical Equilibrium: At a given temperature, a chemical system at equilibrium reaches a state where the ratio of reactant and product concentrations is constant.
Heterogeneous Equilibrium: Equilibrium involving multiple phases (e.g., evaporation of ethanol).
Homogeneous Equilibrium: Equilibrium where all reactants are in the same phase.
Equilibrium Constant (Keq):
- For a given reaction at a given temperature, $K_{eq}$ is constant regardless of initial reactant/product concentrations.
- K > 1: Products are favored.
- K < 1: Reactants are favored.

Essential Question: Which various factors affect chemical equilibrium? How does Le Châtelier’s principle apply to equilibrium systems?
Vocabulary: Le Châtelier's principle.
Le Châtelier’s Principle: If a stress is applied to a system at equilibrium, the system shifts to relieve the stress.
Stresses include:
- Adding or removing reactants/products: Equilibrium shifts to counteract the change.
- Change in pressure: Affects equilibrium, especially in gaseous systems.
- Change in temperature: For example:
  - $CO(g) + 3H<em>2(g) \rightleftharpoons CH</em>4(g) + H_2O(g) AH° = −206.5 kJ$
  - $N<em>2O</em>4(g) \rightleftharpoons 2NO_2(g) AH° = 57.2 kJ$
- Change in catalyst