AP Chemistry Chapter 13: Chemical Equilibrium

Vocabulary flashcards covering core chemical equilibrium concepts, equilibrium expressions, the reaction quotient, and Le Chatelier's principle from Chapter 13.

Equilibrium Constant Expression

A mathematical relationship describing the concentrations of reactants and products at equilibrium, which remain constant.

Magnitude of the Equilibrium Constant ($K$)

A measure of the extent of a reaction, defined by $K = \frac{[\text{Products}]}{[\text{Reactants}]}$; smaller values of $K$ indicate a greater concentration of reactants relative to products at equilibrium.

Chemical Equilibrium

The state of a reaction where the forward reaction rate equals the reverse reaction rate, resulting in constant concentrations of reactants and products.

Temperature Dependence of $K$

The chemical principle establishing that only changing the temperature can change the numerical value of the equilibrium constant $K$.

Reaction Quotient ($Q$)

A ratio comparing product and reactant concentrations at any given point; when $Q < K$, there are too few products compared to equilibrium, causing the reaction to shift to the right.

Law of Mass Action

The rule used to determine the equilibrium expression by taking the ratio of product concentrations to reactant concentrations, each raised to the power of its stoichiometric coefficient.

Heterogeneous Equilibrium Inclusion Rule

The principle stating that pure solids and pure liquids are omitted from the equilibrium constant expression because their concentrations do not change.

Le Chatelier's Principle: Volume Decrease

A disturbance where decreasing the container volume increases pressure, causing the equilibrium to shift toward the side with fewer moles of gas to relieve the pressure.

Le Chatelier's Principle: Temperature Increase in Exothermic Reactions

A disturbance in an exothermic reaction ($\Delta H = -46.6\,kJ$) where increasing temperature causes the system to shift to the left to consume the added heat.

Le Chatelier's Principle: Removal of Product

A disturbance where removing a gaseous product causes $Q < K$, driving the system to shift toward the right to replace the substance that was removed.

Le Chatelier's Principle: Addition of an Inert Gas

An adjustment such as adding helium ($He(g)$) that causes no shift in the equilibrium position because the inert gas is not part of the reaction equation.

Equilibrium Approximation ($x \ll [\text{initial}]$)

A mathematical simplification used when $K$ is very small, allowing the change in concentration ($x$) to be neglected relative to the initial concentration.