Equilibrium (6)

MCAT General Chemistry Review 2025-2026

Reversible Reactions

eventually reach a state in which energy is minimized and entropy is maximized

Dynamic

chemical equilibria are this—the reactions are still occurring, just at a constant rate

Law of Mass Action

gives the expression for the equilibrium constant, Keq. The reaction quotient, Q, has the same form but can be calculated at any concentrations of reactants and products

Q

is a calculated value that relates the reactant and product concentrations at any given time during a reaction

Keq

is the ratio of products to reactants at equilibrium, with each species raised to its stoichiometric coefficient. This for a reaction is constant at a constant temperature

Do Not; Do

pure solids and liquids ______ appear in the law of mass action while gases and aqueous species _____

<; Forward

if Q ___ Keq, delta G < 0, and the reaction proceeds in the ______ direction

=; Dynamic Equilibrium

if Q ___ Keq, delta G = 0, and the reaction is in _________

>; Reverse

if Q ___ Keq, delta G > 0, and the reaction proceeds in the _______ direction

>

if Keq ___ 1, the products are present in greater concentration at equilibrium

~

if Keq ___ 1, products and reactants are both present at equilibrium at reasonably similar levels

<

if Keq ___ 1, the reactants are present in greater concentration at equilibrium

< < <

if Keq ___ 1, the amount of reactants that have been converted to products can be considered negligible in comparison to the initial concentration of reactants

Le Chatelier’s Principle

states that when a chemical system experiences a stress, it will react so as to restore equilibrium

Right

increasing concentration of reactants or decreasing the concentration of products will shift the reaction to the ______

Left

increasing the concentration of products or decreasing the concentration of reactants will shift the reaction to the ______

Increasing; Fewer

_______ pressure on a gaseous system (decreasing its volume) will shift the reaction toward the side with _______ moles of gas

Decreasing; More

________ pressure on a gaseous system (increasing its volume) will shift the reaction toward the side with ______ moles of gas

Right

increasing the temperature of an endothermic reaction or decreasing the temperature of an exothermic reaction will shift the reaction to the _______

Left

decreasing the temperature of an endothermic reaction or increasing the temperature of an exothermic reaction will shift the reaction to the _________

Kinetic Products

are higher in free energy and can form at lower temperatures. These are sometimes termed “fast” products because they can form more quickly under such conditions

Thermodynamic Products

are lower in free energy and are therefore more stable. Despite proceeding more slowly, this is more spontaneous (more negative delta G)