OpenStax Chemistry 2e Chapter 13

Chemical equilibrium

A state where the rates of the forward and reverse reactions are equal.

Dynamic equilibrium

A condition in which the forward and reverse reactions occur at the same rate, resulting in constant concentrations of reactants and products.

Equilibrium constant (K)

The value of the reaction quotient when the reaction is at equilibrium at a specific temperature.

Reaction quotient (Q)

A mathematical expression showing the ratio of products to reactants at any point in a reaction.

Kc

Equilibrium constant expressed using molar concentrations.

Kp

Equilibrium constant expressed using partial pressures.

Law of mass action

At a given temperature, the reaction quotient of a system at equilibrium is constant.

Qc = [C]ⁿ[D]ⁿ / [A]ⁿ[B]ⁿ

The equation for the reaction quotient using concentrations.

Qp = (P_C)ⁿ(P_D)ⁿ / (P_A)ⁿ(P_B)ⁿ

The equation for the reaction quotient using partial pressures.

Kp = Kc (RT)^Δn

The equation relating Kp and Kc for gas-phase reactions.

Δn

Change in moles of gas (moles of gaseous products - moles of gaseous reactants).

R

Ideal gas constant, 0.0821 L·atm/mol·K.

Q < K

The reaction proceeds forward to reach equilibrium.

Q > K

The reaction proceeds in reverse to reach equilibrium.

Q = K

The reaction is at equilibrium.

Reversible reaction

A reaction that can proceed in both forward and reverse directions.

Homogeneous equilibrium

Equilibrium where all reactants and products are in the same phase.

Heterogeneous equilibrium

Equilibrium involving reactants and products in different phases.

Coupled equilibria

Two or more equilibria sharing common species.

Le Châtelier's Principle

A principle stating that a system at equilibrium responds to stress by shifting to counteract the change.

Effect of adding reactant

Shifts equilibrium to the right (toward products).

Effect of removing reactant

Shifts equilibrium to the left (toward reactants).

Effect of adding product

Shifts equilibrium to the left (toward reactants).

Effect of removing product

Shifts equilibrium to the right (toward products).

Decreasing volume

Increases pressure and shifts equilibrium toward fewer moles of gas.

Increasing volume

Decreases pressure and shifts equilibrium toward more moles of gas.

Equal moles of gas

Volume change has no effect on equilibrium.

Endothermic reaction

Heat is a reactant; increasing temperature shifts equilibrium right.

Exothermic reaction

Heat is a product; increasing temperature shifts equilibrium left.

Catalyst effect

Speeds up both forward and reverse reactions but does not change equilibrium position or K.

ICE Table

A table used to calculate equilibrium concentrations using Initial, Change, and Equilibrium values.

Quadratic formula

x = [-b ± √(b² - 4ac)] / 2a — used to solve equilibrium problems.

Equilibrium and temperature

The only factor that can change the value of the equilibrium constant (K).

Rate constant

Intrinsic capacity of a molecule to undergo change.

Physical equilibrium

An equilibrium involving physical processes (e.g., phase changes).

Br₂(l) ⇌ Br₂(g)

Example of physical equilibrium through vaporization and condensation.

Equilibrium shift

Occurs when a system experiences changes in concentration, pressure, or temperature.