Words (or words that have the same definition) The definition is case sensitive (Optional) Image to display with the definition [Not displayed in Glossary, only in pop-up on pages] (Optional) Caption for Image (Optional) External or Internal Link (Optional) Source for Definition (Eg. "Genetic, Hereditary, DNA ...") (Eg. "Relating to genes or heredity") NaN The infamous double helix https://bio.libretexts.org/ CC-BY-SA; Delmar Larsen Word(s) Definition Image Caption Link Source activated complex (also, transition state) unstable combination of reactant species formed during a chemical reaction NaN NaN NaN NaN activation energy (Ea) minimum energy necessary in order for a reaction to take place NaN NaN NaN NaN Arrhenius equation mathematical relationship between a reaction’s rate constant, activation energy, and temperature NaN NaN NaN NaN average rate rate of a chemical reaction computed as the ratio of a measured change in amount or concentration of substance to the time interval over which the change occurred NaN NaN NaN NaN bimolecular reaction elementary reaction involving two reactant species NaN NaN NaN NaN catalyst substance that increases the rate of a reaction without itself being consumed by the reaction NaN NaN NaN NaN collision theory model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics NaN NaN NaN NaN elementary reaction reaction that takes place in a single step, precisely as depicted in its chemical equation NaN NaN NaN NaN frequency factor (A) proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation NaN NaN NaN NaN half-life of a reaction (tl/2) time required for half of a given amount of reactant to be consumed NaN NaN NaN NaN heterogeneous catalyst catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur NaN NaN NaN NaN homogeneous catalyst catalyst present in the same phase as the reactants NaN NaN NaN NaN initial rate instantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun) NaN NaN NaN NaN instantaneous rate rate of a chemical reaction at any instant in time, determined by the slope of the line tangential to a graph of concentration as a function of time NaN NaN NaN NaN integrated rate law equation that relates the concentration of a reactant to elapsed time of reaction NaN NaN NaN NaN intermediate species produced in one step of a reaction mechanism and consumed in a subsequent step NaN NaN NaN NaN method of initial rates common experimental approach to determining rate laws that involves measuring reaction rates at varying initial reactant concentrations NaN NaN NaN NaN molecularity number of reactant species involved in an elementary reaction NaN NaN NaN NaN overall reaction order sum of the reaction orders for each substance represented in the rate law NaN NaN NaN NaN rate constant (k) proportionality constant in a rate law NaN NaN NaN NaN rate expression mathematical representation defining reaction rate as change in amount, concentration, or pressure of reactant or product species per unit time NaN NaN NaN NaN rate law (also, rate equation) (also, differential rate laws) mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants NaN NaN NaN NaN rate of reaction measure of the speed at which a chemical reaction takes place NaN NaN NaN NaN rate-determining step (also, rate-limiting step) slowest elementary reaction in a reaction mechanism; determines the rate of the overall reaction NaN NaN NaN NaN reaction diagram used in chemical kinetics to illustrate various properties of a reaction NaN NaN NaN NaN reaction mechanism stepwise sequence of elementary reactions by which a chemical change takes place NaN NaN NaN NaN reaction order value of an exponent in a rate law (for example, zero order for 0, first order for 1, second order for 2, and so on) NaN NaN NaN NaN termolecular reaction elementary reaction involving three reactant species NaN NaN NaN NaN unimolecular reaction elementary reaction involving a single reactant species NaN NaN NaN NaN