Chemistry 132 NTRates of ReactionPowerPoint PresentationReviewReaction MechanismsElementary ReactionsSlide 7Slide 8A Problem To ConsiderSlide 10Slide 11Slide 12Slide 13Slide 14MolecularitySlide 16Rate Equations for Elementary ReactionsSlide 18Slide 19Slide 20Slide 21Slide 22Slide 23Rate Laws and Mechanandand andismsRate Laws and MechanandismsRate Determining StepSlide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39CatalystsSlide 41Slide 42Figure 13.17 Comparison of activation energies in the uncatalyzed and catalyzed decomposition of ozone.Slide 44Slide 45Figure 13.17 Automobile catalytic converter.Enzyme CatalysisKey EquationsOperational SkillsSlide 5011111Chemistry 132 NTNothing great was ever achieved without enthusiasm.Ralph Waldo Emerson22222Rates of ReactionChapter 13Module 4Sections 13.7, 13.8, and 13.9The burning of steel wool3333344444ReviewCollision Theory and the rate constant.The Arrhenius equation.55555Reaction MechanismsEven though a balanced chemical equation may give the ultimate result of a reaction, what actually happens in the reaction may take place in several steps.This “pathway” the reaction takes is referred to as the reaction mechanism.The individual steps in the larger overall reaction are referred to as elementary reactions.66666Elementary ReactionsEach elementary step is a singular molecular event resulting in the formation of products.The set of elementary reactions that result in an overall reaction is called the reaction mechanism.A reaction intermediate is a species produced during a reaction but is re-consumed in a later step. Consequently, it will not appear in the overall reaction.77777Elementary ReactionsConsider the reaction of nitrogen dioxide with carbon monoxide.)g(CO)g(NO)g(CO)g(NO22This reaction is believed to take place in two steps.)g(NO)g(NO)g(NO)g(NO322(elementary reaction))g(CO)g(NO)g(CO)g(NO223(elementary reaction)88888Elementary ReactionsEach step is a singular molecular event resulting in the formation of products.The overall chemical equation is obtained by adding the two steps together and canceling any species common to both sides.)g(CO)g(NO)g(CO)g(NO223)g(NO)g(NO)g(NO)g(NO322)g(CO)g(NO)g(CO)g(NO22Overall reaction99999A Problem To ConsiderCarbon tetrachloride is obtained by the chlorination of chloroform, CHCl3. The mechanism for the gas phase reaction is:Obtain the net, or overall, chemical equation from this mechanism.)g(Cl2 )g(Cl2)g(CCl)g(HCl)g(CHCl)g(Cl33)g(CCl)g(CCl)g(Cl431010101010A Problem To ConsiderCarbon tetrachloride is obtained by the chlorination of chloroform, CHCl3. The mechanism for the gas phase reaction is:The first step produces two Cl atoms (a reaction intermediate). One Cl atom is used in the second step and another is used in the third step. )g(Cl2 )g(Cl2)g(CCl)g(HCl)g(CHCl)g(Cl33)g(CCl)g(CCl)g(Cl431111111111A Problem To ConsiderCarbon tetrachloride is obtained by the chlorination of chloroform, CHCl3. The mechanism for the gas phase reaction is:Thus, all Cl atoms cancel)g(Cl2 )g(Cl2)g(CCl)g(HCl)g(CHCl)g(Cl33)g(CCl)g(CCl)g(Cl431212121212A Problem To ConsiderCarbon tetrachloride is obtained by the chlorination of chloroform, CHCl3. The mechanism for the gas phase reaction is:Similarly, the intermediate CCl3, produced in the second step, is used up in the third step.)g(Cl2 )g(Cl2)g(CCl)g(HCl)g(CHCl)g(Cl33)g(CCl)g(CCl)g(Cl431313131313A Problem To ConsiderCarbon tetrachloride is obtained by the chlorination of chloroform, CHCl3. The mechanism for the gas phase reaction is:You can cancel both CCl3 species.)g(Cl2 )g(Cl2)g(CCl)g(HCl)g(CHCl)g(Cl33)g(CCl)g(CCl)g(Cl431414141414A Problem To ConsiderCarbon tetrachloride is obtained by the chlorination of chloroform, CHCl3. The mechanism for the gas phase reaction is:)g(Cl2 )g(Cl2)g(CCl)g(HCl)g(CHCl)g(Cl33)g(CCl)g(CCl)g(Cl43The overall equation.)g(CCl)g(HCl)g(CHCl)g(Cl432(see Exercise 13.8 and Problem 13.69)1515151515MolecularityWe can classify reactions according to their molecularity, that is, the number of molecules that must collide for the elementary reaction to occur.A unimolecular reaction involves only one reactant molecule.A bimolecular reaction involves the collision of two reactant molecules.A termolecular reaction requires the collision of three reactant molecules.1616161616MolecularityWe can classify reactions according to their molecularity, that is, the number of molecules that must collide for the elementary reaction to occur.Higher molecularities are rare because of the small statistical probability that four or more molecules would all collide at the same instant.1717171717Rate Equations for Elementary ReactionsSince a chemical reaction may occur in several steps, there is no easy relationship between its overall reaction and its rate law.However, for elementary reactions (an individual single-step) the rate is proportional to the concentrations of all reactant molecules involved.1818181818Rate Equations for Elementary ReactionsFor example, consider the generic (elementary) equation below.products A The rate is dependent only on the concentration of A, that is;k[A] Rate 1919191919Rate Equations for Elementary ReactionsHowever, for the elementary reactionproducts B A the rate is dependent on both the concentration of A and B.k[A][B] Rate 2020202020Rate Equations for Elementary ReactionsFor a termolecular elementary reactionproducts C B A the rate is dependent on the populations of all three participants.k[A][B][C] Rate 2121212121Rate Equations for Elementary ReactionsNote that if two molecules of a given reactant are required, it appears twice in the rate law. For example, the elementary reactionproducts B 2A would have the rate law:[B]k[A] Rate2k[A][A][B] Rate or2222222222A Problem To ConsiderOzone is converted to O2 by NO in a single step (that is, it is an elementary reaction).223NOONOO Write the rate law for this elementary reaction.The rate law equation can be written directly from the elementary reaction (but only for an elementary reaction).NO]][k[ORate3(see Exercise 13.10 and Problem 13.73)2323232323Rate Equations for Elementary ReactionsSo, in essence, for an elementary reaction, the coefficient of each reactant becomes the power to which it is raised in the rate