AP Chemistry Chapter 13: Chemical Equilibrium

A set of vocabulary flashcards reviewing the concepts of chemical equilibrium, the reaction quotient Q, equilibrium constant expressions, and Le Chatelier's principle based on the Chapter 13 Pre-Test #2 solutions.

Equilibrium Constant Expression ($K$)

A mathematical relationship that describes the concentration of reactants and products at equilibrium, represented as $K = \frac{[\text{PRODUCTS}]}{[\text{REACTANTS}]}$.

Reaction Quotient ($Q$)

The ratio calculated from initial reactant and product concentrations using the formula $Q = \frac{[\text{PRODUCTS}]}{[\text{REACTANTS}]}$ to determine the direction the system will shift to reach equilibrium.

Condition for $Q < K$

The condition where the reaction quotient is less than the equilibrium constant; more products are needed, and the reaction shifts toward the products (right).

Condition for $Q > K$

The condition where the reaction quotient is greater than the equilibrium constant; less products are needed, and the reaction shifts toward the reactants (left).

Chemical Equilibrium

The state reached when the concentrations of the reactants and the products do not change and the opposing forward and reverse reaction rates are equal.

Magnitude of the Equilibrium Constant

The relative size of $K$; a larger equilibrium constant indicates that the concentration of product(s) will be larger for a given concentration of reactant(s) at equilibrium.

Law of Mass Action for Heterogeneous Systems

The rule establishing that pure solids and liquids are omitted from equilibrium constant expressions because their concentrations remain constant.

$K_c$ Expression for $3H_{2(g)} + 2As_{(s)} \rightleftharpoons 2AsH_{3(g)}$

The molar concentration equilibrium expression for this reaction, written as $K_c = \frac{[AsH_3]^2}{[H_2]^3}$.

$K_p$ Expression for $CuSO_4 \times 4H_2O_{(s)} \rightleftharpoons CuSO_{4(s)} + 4H_2O_{(g)}$

The partial pressure equilibrium expression for this reaction, written as $K_p = P_{H_2O}^4$.

Temperature Dependence of $K$

The principle that the numerical value of the equilibrium constant $K$ does not change when species are added or removed, changing only when the system temperature changes.

Decreasing Container Volume

An adjustment that increases total system pressure, causing an equilibrium system to shift toward the side with fewer moles of gas to reduce the added pressure.

Increasing Temperature in an Endothermic Reaction

An adjustment in a reaction where $\Delta H > 0$ (heat acts as a reactant) that shifts the equilibrium position to the right and causes the value of $K$ to increase.

Adding a Product to an Equilibrium System

A disturbance resulting in $K < Q$ that shifts the reaction to the left to consume some of the added product without changing $K$.

Removing a Product from an Equilibrium System

A disturbance resulting in $K > Q$ that shifts the reaction to the right to regenerate some of the lost product without changing $K$.

Addition of Helium (Inert Gas)

An adjustment that causes no shift in the equilibrium position because helium is an inert gas that is not involved in the chemical reaction.

Small $x$ Approximation

A simplifying assumption used when the equilibrium constant is very small ($K \ll 1$), allowing the change $x$ to be neglected relative to initial concentrations ($x \ll [\text{initial}]$).