Learning Goal: Order and rate law of a reaction To understand how elementary steps make up a mechanism and how the rate law for an elementary step can be determined. The overall order of an elementary step directly corresponds to its molecularity. Both steps in this example are second order because they are each bimolecular. Furthermore, the rate law can be determined directly from the number of each type of molecule in an elementary step. For example, the rate law for step 1 is Very often, a reaction does not tell us the whole story. For instance, the reaction rate = k[NO22 NO(9) + CO(9)→NO(g)+ CO2(9) The exponent "2" is used because the reaction involves two NO2molecules. The rate law for step 2 is does not involve a collision between an NO2molecule and a COmolecule. Based on experimental data at moderate temperatures, this reaction is thought to occur in the following two steps: rate = k[NO3"COj'= k[NO3[CO] because the reaction involves only one molecule of each reactant the exponents are omitted. 1. NO2(9) + NO2(9)→NO3(9)+NO(9) 2. NO3(9) + CO(g)→CO2(9)+NO2{9) Analyzing a new reaction Each individual step is called an elementary step. Together, these elementary steps are called the reaction mechanism. Consider the following elementary steps that make up the mechanism of a certain reaction: Overall, the resulting reaction is 1. 2X→Y+Z 2. Y+ 2L→M+Z NO19) + CO(9)→NO(g)+CO2(9) Notice that in the elementary steps NO3appears both as a product and then as a reactant; therefore it cancels out of the final chemical equation. NOzis called a reaction intermediate. Also notice that 2 molecules of NO2appear in the reactants of the first step and 1 molecule of NO2appears as product of the second step, the net effect leaves only 1 molecule of NO2as a reactant in the net equation. • Part A What is the overall reaction? Express your answer as a chemical equation. Molecularity is the proper term for "how the molecules collide" in a reaction. For example, step 1 is bimolecular because it involves the collision of two molecules. Step 2 is also bimolecular for the same reason. Unimolecular reactions involve only one molecule in the reactants. Though rare, collisions among three molecules can occur. Such a reaction would be called termolecular. » View Available Hint(s) 2X + 2L→M +2Z Submit Previous Answers v Correct • Part B Which species is a reaction intermediate? » View Available Hint(s) Submit Previous Answers v Correct Part C What is the rate law for step 1 of this reaction? Express your answer in standard MasteringChemistry notation. For example, if the rate law is k[A][C|type k* [A] * [c]^3. » View Available Hint(s) Rate = Submit Request Answer Part D What is the rate law for step 2 of this reaction? Express your answer in standard MasteringChemistry notation. For example, if the rate law is k[A][C]type k* [A] * [c]^3. , View Available Hint(s) Rate =

Learning Goal: Order and rate law of a reaction To understand how elementary steps make up a mechanism and how the rate law for an elementary step can be determined. The overall order of an elementary step directly corresponds to its molecularity. Both steps in this example are second order because they are each bimolecular. Furthermore, the rate law can be determined directly from the number of each type of molecule in an elementary step. For example, the rate law for step 1 is Very often, a reaction does not tell us the whole story. For instance, the reaction rate = k[NO22 NO(9) + CO(9)→NO(g)+ CO2(9) The exponent "2" is used because the reaction involves two NO2molecules. The rate law for step 2 is does not involve a collision between an NO2molecule and a COmolecule. Based on experimental data at moderate temperatures, this reaction is thought to occur in the following two steps: rate = k[NO3"COj'= k[NO3[CO] because the reaction involves only one molecule of each reactant the exponents are omitted. 1. NO2(9) + NO2(9)→NO3(9)+NO(9) 2. NO3(9) + CO(g)→CO2(9)+NO2{9) Analyzing a new reaction Each individual step is called an elementary step. Together, these elementary steps are called the reaction mechanism. Consider the following elementary steps that make up the mechanism of a certain reaction: Overall, the resulting reaction is 1. 2X→Y+Z 2. Y+ 2L→M+Z NO19) + CO(9)→NO(g)+CO2(9) Notice that in the elementary steps NO3appears both as a product and then as a reactant; therefore it cancels out of the final chemical equation. NOzis called a reaction intermediate. Also notice that 2 molecules of NO2appear in the reactants of the first step and 1 molecule of NO2appears as product of the second step, the net effect leaves only 1 molecule of NO2as a reactant in the net equation. • Part A What is the overall reaction? Express your answer as a chemical equation. Molecularity is the proper term for "how the molecules collide" in a reaction. For example, step 1 is bimolecular because it involves the collision of two molecules. Step 2 is also bimolecular for the same reason. Unimolecular reactions involve only one molecule in the reactants. Though rare, collisions among three molecules can occur. Such a reaction would be called termolecular. » View Available Hint(s) 2X + 2L→M +2Z Submit Previous Answers v Correct • Part B Which species is a reaction intermediate? » View Available Hint(s) Submit Previous Answers v Correct Part C What is the rate law for step 1 of this reaction? Express your answer in standard MasteringChemistry notation. For example, if the rate law is k[A][C|type k* [A] * [c]^3. » View Available Hint(s) Rate = Submit Request Answer Part D What is the rate law for step 2 of this reaction? Express your answer in standard MasteringChemistry notation. For example, if the rate law is k[A][C]type k* [A] * [c]^3. , View Available Hint(s) Rate =

Organic Chemistry: A Guided Inquiry

2nd Edition

ISBN:9780618974122

Author:Andrei Straumanis

Publisher:Andrei Straumanis

Chapter15: Radical Reactions

Section: Chapter Questions

Problem 20CTQ

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