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Chemistry LibreTexts

12.8: Key Terms

  • Page ID
    415223
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    Example and Directions
    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")The infamous double helix https://bio.libretexts.org/CC-BY-SA; Delmar Larsen
    Glossary Entries
    Word(s)DefinitionImageCaptionLinkSource
    activated complex(also, transition state) unstable combination of reactant species formed during a chemical reaction    
    activation energy (Ea)minimum energy necessary in order for a reaction to take place    
    Arrhenius equationmathematical relationship between a reaction’s rate constant, activation energy, and temperature    
    average raterate 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    
    bimolecular reactionelementary reaction involving two reactant species    
    catalystsubstance that increases the rate of a reaction without itself being consumed by the reaction    
    collision theorymodel that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics    
    elementary reactionreaction that takes place in a single step, precisely as depicted in its chemical equation    
    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    
    half-life of a reaction (tl/2)time required for half of a given amount of reactant to be consumed    
    heterogeneous catalystcatalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur    
    homogeneous catalystcatalyst present in the same phase as the reactants    
    initial rateinstantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun)    
    instantaneous raterate 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    
    integrated rate lawequation that relates the concentration of a reactant to elapsed time of reaction    
    intermediatespecies produced in one step of a reaction mechanism and consumed in a subsequent step    
    method of initial ratescommon experimental approach to determining rate laws that involves measuring reaction rates at varying initial reactant concentrations    
    molecularitynumber of reactant species involved in an elementary reaction    
    overall reaction ordersum of the reaction orders for each substance represented in the rate law    
    rate constant (k)proportionality constant in a rate law    
    rate expressionmathematical representation defining reaction rate as change in amount, concentration, or pressure of reactant or product species per unit time    
    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    
    rate of reactionmeasure of the speed at which a chemical reaction takes place    
    rate-determining step(also, rate-limiting step) slowest elementary reaction in a reaction mechanism; determines the rate of the overall reaction    
    reaction diagramused in chemical kinetics to illustrate various properties of a reaction    
    reaction mechanismstepwise sequence of elementary reactions by which a chemical change takes place    
    reaction ordervalue of an exponent in a rate law (for example, zero order for 0, first order for 1, second order for 2, and so on)    
    termolecular reactionelementary reaction involving three reactant species    
    unimolecular reactionelementary reaction involving a single reactant species    

    12.8: Key Terms is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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