chapter 13

chapter 13 - Chemical Kinetics Chemical Kinetics Reaction...

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1 Chemical Kinetics Chemical Kinetics Reaction Mechanisms Some definitions kinetics – The study of reaction rates and the rates are affected by different factors. Mechanism - A step by step description of how a reaction occurs. chemical kinetics is just one of the tools chemists use in order to determine the mechanism of chemical processes.
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2 Kinetics – the study of rates of chemical reactions - and how they are affected In order to study the rates of a chemical reaction we must be able to follow the reaction. reactants products  We can follow the rate of this reaction by measuring either the increase in the concentration of product per unit time or The decrease in the concentration of reactant per unit time The rate of disappearance of reactants The rate of appearance of products Reaction Rate: The change in the concentration of a reactant or a product with time (M/s). Reactant Products A B Rate   [ A ] t Rate [ B ] t The rate of disappearance of A must be equal to the rate of appearance of B
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3 Reaction Rate: The change in the concentration of a reactant or a product with time (M/s). Reactant Products 1A 2B [ ] 1 [ ] Rate Rate 2 AB tt    The rate of disappearance of A must be equal to one half the rate of appearance of B Consider the decomposition of N 2 O 5 to give NO 2 and O 2 : 2 N 2 O 5 (g) 4 NO 2 (g) + O 2 (g) The rate of disappearance of N 2 O 5 should by twice the rate of appearance of O 2 and half the rate of appearance of NO 2
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4 Rate of appearance of O 2 at 300-400 .000009 Rate of disappearance of N 2 O 5 is 0.000019 Rate of appearance of NO 2 is .000037 These rates are not constant, notice that the rates decrease with time. Rate Law The first goal in studying the kinetics of a chemical reaction is to determine the rate law. The rate law describes the dependence of the reaction rate on the concentration of each reactant. There are various methods of doing this. Reaction order is determined experimentally: 1. By the initial rate method (the book calls this by inspection). 2. By plotting the integrated rate expression
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5 Rate Law: Shows the relationship of the rate of a reaction to the rate constant and the concentration of the reactants raised to some powers.
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chapter 13 - Chemical Kinetics Chemical Kinetics Reaction...

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