CHEM 1A Study Guide - Midterm Guide: Elementary Reaction, Reaction Mechanism, Reaction Intermediate

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Elementary reactions elementary reactions : reaction mechanism : an individual step in a proposed reaction mechanism a sequence of elementary reactions or steps that is believed to take place as reactants are transformed into products. Rate measurements can be used to eliminate some mechanisms example : 02 + 03 oz + oz + oz. I t oz o , attacks. + o , reaction intermediate : a species that is produced and consumed during a reactant but does not appear in the overall chemical equation. Stoichiometric coefficients are not used for elementary reactions: elementary reactions are classified according to molecularity molecularity : number of. Unimolecular reaction : an elementary reaction in which a single reactant species changes into reactant molecules taking part in each step products molecularity = i example : 2 - step mechanism of ozone decomposition ( above - 03 oz t o) biomolecular reaction : an elementary reaction in which 2 species come together.

Related Questions

3. The gas-phase reaction

2 NO + O₂ â 2 NO₂ has the observed rate law: R = k[NO]²[O₂].

Devise some mechanisms (sequence of elementary reaction steps) that lead to the observed rate law if you assume that there is a rate-determining step.

Hint: a trimolecular reaction is not the only possibility. Consider the possibility that the first step is actually bimolecular, either of two NO molecules colliding and or of NO and O₂ colliding. In these two possibilities, assume that the product of the bimolecular first step is a kinetic intermediate, a species that does not appear in the overall reaction stochiometry.

If you assume that the intermediate then reacts in a rate-limiting bimolecular reaction with one of the reactants to form the overall NO₂ product, show in each of these cases that you get the overall rate law.

Order and rate law of a reaction The overall order of anelementary step directly corresponds to its molecularity. Bothsteps in this example are second order because they are eachbimolecular. Furthermore, the rate law can be determined directlyfrom the number of each type of molecule in an elementary step. Forexample, the rate law for step 1 is rate=k[NO2]2 The exponent "2"is used because the reaction involves two NO2 molecules. The ratelaw for step 2 is rate=k[N2O4]1[CO]1=k[N2O4][CO] because thereaction involves only one molecule of each reactant. Analyzing anew reaction Consider the following elementary steps that make upthe mechanism of a certain reaction: 2A?B+C B+D?E+C

Part A What is the overall reaction? Express your answer as achemical equation.

Part B

Which species is a reaction intermediate?

Part C

What is the rate law for step 1 of this reaction?

Express your answer in standard MasteringChemistry notation. Forexample, if the rate law is k[A][C]3 type k*[A]*[C]^3.

Part D

What is the rate law for step 2 of this reaction?

Express your answer in standard MasteringChemistry notation. Forexample, if the rate law is k[A][C]3 type k*[A]*[C]^3.

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CHEM 1A Study Guide - Midterm Guide: Elementary Reaction, Reaction Mechanism, Reaction Intermediate

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