Reaction rate constant

A proportionality constant in a chemical reaction’s rate law, relating reactant concentrations to reaction rate at a specified temperature. Its units depend on the reaction’s overall order.

Rate law: An equation relating a reaction’s rate to reactant concentrations, usually through experimentally determined exponents. The rate constant is the coefficient that makes a rate law quantitative.
Reaction rate: The change in reactant or product concentration per unit time during a chemical reaction. The rate constant links this measured quantity to concentrations through the rate law.
Integrated rate law: An equation giving concentration as a function of time for a reaction with a specified rate law. It uses the rate constant to predict how concentrations evolve over time.
Equilibrium constant: A thermodynamic ratio of product and reactant activities at chemical equilibrium. Unlike a rate constant, it describes equilibrium composition rather than reaction speed.
Reaction order: The exponent of a species’ concentration in a rate law; the exponents sum to the overall order. Overall order determines the rate constant’s units and how concentration affects rate.
Concentration: The amount of a substance per volume of solution or mixture. Concentration values enter the rate law and determine the rate associated with a given constant.
Half-life: The time required for a reactant concentration or quantity to fall to half its initial value. For first-order reactions, half-life is determined directly by the rate constant.
Specific rate constant: A traditional name for the coefficient in a rate law, emphasizing its value under specified conditions. The label distinguishes the constant from the changing reaction rate itself.
Collision theory: A model explaining reaction rates through collisions with sufficient energy and suitable molecular orientation. It connects molecular encounters to the frequency factor underlying many rate constants.
Stoichiometry: The quantitative relationships among reactants and products in a chemical equation. Stoichiometric coefficients define reaction-rate conventions but do not generally determine rate-law exponents.

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