Chemical Equilibrium Practice Flashcards

These vocabulary flashcards cover the fundamental principles of Chemical Equilibrium from Chapter 14, including the Law of Mass Action, heterogeneous and homogeneous equilibria, and Le Châtelier’s Principle.

Equilibrium

A state in which there are no observable changes as time goes by.

Chemical Equilibrium

A state achieved when the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant.

Physical equilibrium

An equilibrium that occurs during a physical change, such as the phase change between liquid water and steam: $\text{H}_2\text{O} (l) \rightleftharpoons \text{H}_2\text{O} (g)$.

Law of Mass Action

For a reversible reaction at equilibrium and a constant temperature, a certain ratio of reactant and product concentrations has a constant value $K$, expressed as $K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ for the reaction $aA + bB \rightleftharpoons cC + dD$.

Homogenous equilibrium

Applies to reactions in which all reacting species are in the same phase.

$K_p$ and $K_c$ Relationship

The mathematical relationship defined by the formula $K_p = K_c(RT)^{\triangle n}$, where $\triangle n$ is the moles of gaseous products minus the moles of gaseous reactants.

Heterogenous equilibrium

Applies to reactions in which reactants and products are in different phases.

Equilibrium Constant Expression Exclusions

Concentrations of pure solids, pure liquids, and solvents are not included in the equilibrium constant expression because their concentrations are considered constant.

Equilibrium Constant Dimension

The equilibrium constant is a dimensionless quantity.

Multiple Equilibria Rule

If a reaction is the sum of two or more reactions, the equilibrium constant for the overall reaction is the product of the equilibrium constants of the individual reactions ($K_c = K_c' \times K_c''$).

Reciprocal Rule for Equilibrium

When the equation for a reversible reaction is written in the opposite direction, the equilibrium constant becomes the reciprocal of the original equilibrium constant ($K = \frac{1}{K'}$).

Reaction Quotient ($Q_c$)

A value calculated by substituting initial concentrations into the equilibrium constant expression to determine the direction the system will proceed to reach equilibrium.

$$Q_c > K_c$$

The system proceeds from right to left (toward reactants) to reach equilibrium.

$$Q_c = K_c$$

The system is already at equilibrium.

$$Q_c < K_c$$

The system proceeds from left to right (toward products) to reach equilibrium.

Le Châtelier’s Principle

If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position.

Catalyst Effect on Equilibrium

Lowers the activation energy ($E_a$) for both forward and reverse reactions, allowing the system to reach equilibrium sooner without changing the equilibrium constant ($K$) or shifting the position of equilibrium.

Haber Process

The industrial synthesis of ammonia from nitrogen and hydrogen gas, represented by the reaction $N_2 (g) + 3H_2 (g) \rightleftharpoons 2NH_3 (g)$, where $\Delta H^0 = -92.6\text{ kJ/mol}$.

$$K >> 1$$

Equilibrium lies to the right and favors the products.

$$K << 1$$

Equilibrium lies to the left and favors the reactants.