Le Chatelier's Principle: A principle that states when a chemical system at equilibrium is subjected to a change in one of the conditions (concentration, temperature, or pressure), the system will shift to counteract the change and reestablish equilibrium.
Equilibrium Constant (K): A quantitative measure of the extent of a reaction at equilibrium, defined as the ratio of the concentrations of the products to the concentrations of the reactants, each raised to the power of their stoichiometric coefficients.
Reaction Quotient (Q): The ratio of the actual concentrations of the products to the actual concentrations of the reactants in a chemical system, which can be used to determine whether a reaction is at equilibrium or not.