Today!Kinetics Rate Laws"Finding the order of a reaction!Integrated Rate Laws!What is the concentration as a function of time?!The grand overview of all of the kinetics!rate!aA + bB cC + dD!∆[C]!c∆t!-∆[A]!a∆t!=!=!=!k[A]x[B]y!we are looking only at the rate of the "forward" reaction!This depends only on the concentration of the reactants!measure in experiment! figure out from data!Method of Initial Rates!Experiment [A]o [B]o initial rate (M s-1)!1 0.1M 0.1M 2.73!2 0.15M 0.1M 6.14!3 0.1M 0.2M 2.74!A + 2B C!The reaction is what order in A? - work out on doc cam!Method of Initial Rates!Experiment [A]o [B]o initial rate (M s-1)!1 0.1M 0.1M 2.73!2 0.15M 0.1M 6.14!3 0.1M 0.2M 2.74!A + 2B C!!A. ! !0!!B. ! !1!!C. ! !1.5!!D. ! !2!the reaction is what order in B?!Method of Initial Rates!Experiment [A]o [B]o initial rate (M s-1)!1 0.1M 0.1M 2.73!2 0.15M 0.1M 6.14!3 0.1M 0.2M 2.74!A + 2B C!!A. ! !273 M-1 s-1!!B. ! !27.3 s-1!!C. ! !61.4 s-1!!D. ! !614 M-1 s-1!!E. ! !6.14 M s-1!what is k?!Integrated rate laws!(the concentration as a function of time)!We need a situation in which either!1. The rate law depends on only one reactant!I1. Only one reactant is changing much in concentrations, !so effectively only one concentration is changing!CO(g) + H2O(g) CO2(g) + H2(g)!Both CO and H2O changing at the same time!!CO(g) + H2O(g) CO2(g) + H2(g)!The rate law for this reaction is!rate = k[H2O][CO]!it is first order in H2O and!first order in CO!CO(g) + H2O(g) CO2(g) + H2(g)!What if we started with a whole lot of H2O !compared to CO?!The [H2O] ~ constant (since there is so much of it)!Now we can combine the [H2O] with k!(since both are constant)!and write the rate law as!rate = k[H2O][CO] = k’[CO]!we now say the reaction is pseudo-first order in CO!Integrated rate laws!(the concentration as a function of time)!We need a situation in which either!1. The rate law depends on only one reactant!I1. Only one reactant is changing much in concentrations, !so effectively only one concentration is changing!for example it is first order with respect to A!for example it is pseudo first order with respect to A!Integrated Rate Law!First Order!The rate is proportional to the concentration!of only one reactant. We’ll call it A!rate = !-d[A]!adt!time!stoichiometric!coeficient!= k[A]! then some calculus!Integrated Rate Law!First Order![A] = [A]oe-akt!ln[A] = -akt + ln[A]o!So if you plot ln[A] vs time you get !a straight line with a slope of -ak!Half life!The half-life is the time at which half the initial concentration remains.!What is the approximate half-life for the reaction at the left?!!A. !!200 s!!B. !!400 s!!C. !!1100 s!!D. !!1600 s!Integrated Rate Law!Zero Order!The rate is independent of the concentration!of our reactant A!rate = !-d[A]!adt!time!stoichiometric!coeficient!= k! then some calculus!Zeroth Order![A] = -akt + [A]o!Plot of [A] vs time yields a !straight line with a slope of -ak!Integrated Rate Law!Second Order!The rate is dependent of the concentration!of our reactant A squared!rate = !-d[A]!adt!time!stoichiometric!coeficient!= k[A]2!then some calculus!Integrated Rate Law!Second Order!1/[A] = akt + 1/[A]o!So if you plot 1/[A] vs time you get !a straight line with a slope of ak!Graphically determining the overall order of a reaction!Half Life!Time after which half the material has reacted!Important for first order reactions!as it is independent of the concentration!t1/2 = ln2/k = 0.693/k!Which of the following is a plot of the concentration!of a reactant that is first order?!Which of the following is a plot of the concentration!of a reactant that is zeroth
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