CHEM 104 1st Edition Lecture 13 Chemical kinetics study of rates of reactions and pathways mechanisms from reactants to products Factors that influence reaction rates Concentration of reactants o Higher concentration higher rates Temperature o Higher temperature higher rates Catalysts o Catalyst substance that increases rate of reaction but isn t used up in the reaction is also present after Surface of solid reactant or catalyst o Larger surface areas higher rates o Only applies to heterogeneous reactions Heterogeneous reactions reactants are in different phases Homogeneous reactions reactants are in the same phase Reaction rate change in concentration of a reactant or product per unit time Rate equation change in concentration of product change in time change of concentration of reactant change in time Change in concentration of product product Need to take into account stoichiometry aA bB cC dD Rate 1 a A change in time 1 b B change in time 1 c C change in time 1 d D change in time Reactant product graph below depicts reaction rates showing concentration of reactant over time red and concentration of product over time blue Average rate rate over a time interval Decreases over time Instantaneous rate rate at a single time point Slope of the line tangent to the curve at time t Initial rate instantaneous rate at t 0
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