Ch. 18: Le Chatelier's Principle

Flashcards covering key vocabulary and concepts from Chapter 18 lecture notes.

Reversible Reactions

Reactions that occur simultaneously in both directions, forming products and reforming reactants.

Chemical Equilibrium

A state where there is no net change in the amounts of the components of the system, and the rates of forward and reverse reactions are equal.

Equilibrium Position

Given by the concentrations of the system’s components at equilibrium; arrow direction indicates whether the components on the left or right side of a reversible reaction are at a higher concentration.

Reversibility vs. Reality

Most reactions are reversible to some extent, but one set of components is often so favored at equilibrium that the other set cannot be detected. A catalyst speeds up forward and reverse reactions equally, decreasing the time to establish equilibrium without affecting the amounts of reactants and products.

Equilibrium Expression

A numerical constant that shows the relationship between the amount of product and reactant at equilibrium. It is a ratio of product concentrations to reactant concentrations, with each substance raised to a power equal to the number of moles in the balanced reaction equation.

Keq

The equilibrium constant, representing the ratio of products to reactants at equilibrium. Keq > 1 means products are favored; Keq < 1 means reactants are favored.

Reaction Quotient (Q)

A measure used to determine if a reaction has reached equilibrium by taking a snapshot of the reaction at a given time and comparing it to the equilibrium constant (Keq).

Le Chatelier's Principle

If a stress is applied to a system in dynamic equilibrium, the system changes to relieve the stress. Stresses include changes in temperature, pressure, and concentration of reactants or products.

Concentration & Equilibrium ([Reactant]↑)

If the concentration of a reactant is increased in a system at equilibrium, the reaction will shift toward the products to use up the extra reactant and reestablish equilibrium at a new position.

Concentration & Equilibrium ([Product]↑)

If the concentration of a product is increased in a system at equilibrium, the reaction will shift toward the reactants to use up the extra product and reestablish equilibrium.

Temperature Effects on Equilibrium

The impact of temperature changes depends on whether the process is endothermic or exothermic; Keq is temperature-dependent.

Pressure & Equilibrium (Pressure Increased)

When pressure is increased in a system with gaseous components, the equilibrium shifts to favor the direction that produces fewer gas molecules.

Pressure & Equilibrium (Pressure Decreased)

A decrease in pressure favors the reaction that produces the most molecules; equilibrium shifts to the left.