Definition

1. Noun:
   • A principle in physical chemistry: The equilibrium law is the principle stating that for a reversible chemical reaction at equilibrium, the ratio of the rate of the forward reaction to the rate of the reverse reaction is a constant specific to that reaction at a given temperature. This constant is known as the equilibrium constant.

Usage

The term "equilibrium law" is used in academic and scientific contexts, specifically in chemistry and chemical engineering, to describe this foundational rule governing chemical equilibria. * Understanding the equilibrium law is essential for predicting the concentrations of reactants and products in a closed system. * The experiment demonstrated the equilibrium law by showing the fixed ratio of reaction rates at constant temperature.

Advanced Usage

• Mathematical Expression: The equilibrium law is most commonly expressed not directly with rates, but through the law of mass action, which relates the equilibrium constant () to the concentrations (or partial pressures) of the reactants and products. For a reaction ( aA + bB \rightleftharpoons cC + dD ), the equilibrium constant is ( K = \frac{[C]^c[D]^d}{[A]^a[B]^b} ), where the square brackets denote concentration. This expression is a direct consequence of the principle defined by the equilibrium law.
• Dynamic Equilibrium: The equilibrium law describes a state of dynamic equilibrium, where the forward and reverse reactions continue to occur at equal rates, resulting in no net change in concentrations.

Variants and Related Words

• Law of chemical equilibrium: A synonymous phrase for the equilibrium law.
• Law of mass action: Often used interchangeably, though it specifically provides the mathematical formulation (the equilibrium constant expression) derived from the principle of the equilibrium law.
• Equilibrium constant (K): The numerical constant that results from applying the equilibrium law.

Synonyms

• Law of chemical equilibrium

Related Concepts (Not Phrasal Verbs/Idioms)

• Reversible reaction: A reaction that can proceed in both the forward and reverse directions.
• Le Chatelier's principle: A related principle that predicts how a system at equilibrium responds to changes in concentration, temperature, or pressure. It describes the of a system, while the equilibrium law defines the of equilibrium.
• Homogeneous equilibrium: An equilibrium where all reactants and products are in the same phase (e.g., all gases or all in solution).
• Heterogeneous equilibrium: An equilibrium where reactants and products are in different phases.

Noun

1. (chemistry) the principle that (at chemical equilibrium) in a reversible reaction the ratio of the rate of the forward reaction to the rate of the reverse reaction is a constant for that reaction