Principles of Chemistry II © Vanden BoutTodayKinetics Rate LawsFinding the order of a reactionIntegrated Rate LawsWhat is the concentration as a function of time? Principles of Chemistry II © Vanden BoutThe grand overview of all of the kineticsrateaA + bB cC + dD![C]c!t-![A]a!t===k[A]x[B]ywe are looking only at the rate of the "forward" reactionThis depends only on the concentration of the reactantsmeasure in experiment figure out from data Principles of Chemistry II © Vanden Boutfor example rate = k[NO2]2this reaction is 2nd order in NO2Four Factors that affect a reaction rate1. Concentration of reactantsThis is the "rate" law. It is found by looking at the dataIt depends on the "mechanism"2NO2 2NO + O2 Principles of Chemistry II © Vanden BoutFour Factors that affect a reaction rate2. TemperatureThis changes the rate constant kk = A e-Ea/RTArrhenius Lawpre-factorbarriertemperatureThe higher the temperature the more molecules that have enough energy to make it over the barrierPrinciples of Chemistry II © Vanden Bout2H2(g) + O2(g)2H2O(g)EnergyEa Principles of Chemistry II © Vanden BoutFour Factors that affect a reaction rate3. CatalystThis changes the rate constant k. Reduces Eak = A e-Ea/RTArrhenius Lawpre-factorbarriertemperatureAs the barrier is lower, the rate constant is larger Principles of Chemistry II © Vanden BoutCatalyst Demo Principles of Chemistry II © Vanden BoutFour Factors that affect a reaction rate4. Physical state (solid chunk, dust, gas, ....) This changes the rate constant k. Changes Ak = A e-Ea/RTArrhenius Lawpre-factorbarriertemperaturePrefactor A is the rate constant when T = infinityPrinciples of Chemistry II © Vanden BoutLet's blow something up Principles of Chemistry II © Vanden BoutWhich balloon reacted with a higher rate?" A." " the first one" B." " the second one" C." " they were the same" Principles of Chemistry II © Vanden Bout" A." " the first one" B." " the second oneWhich balloon contained both H2 and O2 Principles of Chemistry II © Vanden Bout" A." " depends on the concentration of oxygen" B." " is independent of the concentration of oxygen" C." " there is no way to know without more dataThe rate for this reactionPrinciples of Chemistry II © Vanden BoutFinding the rate law from initial ratesdetermine NO2- dependence from first two data pointsdetermine NH4+ dependence from second two data points Principles of Chemistry II © Vanden BoutIntegrated Rate LawFirst Order[A] = [A]oe-ktln[A] = -kt + ln[A]oSo if you plot ln[A] vs time you get a straight line with a slope of -k Principles of Chemistry II © Vanden Bout Principles of Chemistry II © Vanden BoutHalf life The half-life is the time at which half the initial concentration remains.what is the half-life for the reaction at the right?" A." " 200 s" B." " 400 s" C." " 1100 s" D." " 1600 sPrinciples of Chemistry II © Vanden BoutZeroth Order[A] = -kt + [A]oPlot of [A] vs time yields a straight line with a slope of -k Principles of Chemistry II © Vanden Bout Principles of Chemistry II © Vanden BoutIntegrated Rate LawSecond Order1/[A] = kt + 1/[A]oSo if you plot 1/[A] vs time you get a straight line with a slope of k Principles of Chemistry II © Vanden BoutPrinciples of Chemistry II © Vanden
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