13654907-42 - Objectives After studying this Unit, you will...

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Chemistry, by its very nature, is concerned with change. Substances with well defined properties are converted by chemical reactions into other substances with different properties. For any chemical reaction, chemists try to find out (a) the feasibility of a chemical reaction which can be predicted by thermodynamics ( as you know that a reaction with Δ G < 0, at constant temperature and pressure is feasible); (b) extent to which a reaction will proceed can be determined from chemical equilibrium; (c) speed of a reaction i.e. time taken by a reaction to reach equilibrium. Along with feasibility and extent, it is equally important to know the rate and the factors controlling the rate of a chemical reaction for its complete understanding. For example, which parameters determine as to how rapidly food gets spoiled? How to design a rapidly setting material for dental filling? Or what controls the rate at which fuel burns in an auto engine? All these questions can be answered by the branch of chemistry, which deals with the study of reaction rates and their mechanisms, called chemical kinetics . The word kinetics is derived from the Greek word ‘kinesis’ meaning movement. Thermodynamics tells only about the feasibility of a reaction whereas chemical kinetics tells about the rate of a reaction. For example, thermodynamic data indicate that diamond shall convert to graphite but in reality the conversion rate is so slow that the change is not perceptible at all. Therefore, most people think After studying this Unit, you will be able to define the average and instantaneous rate of a reaction; express the rate of a reaction in terms of change in concentration of either of the reactants or products with time; distinguish between elementary and complex reactions; differentiate between the molecularity and order of a reaction; define rate constant; discuss the dependence of rate of reactions on concentration, temperature and catalyst; derive integrated rate equations for the zero and first order reactions; determine the rate constants for zeroth and first order reactions; describe collision theory. Objectives Chemical Kinetics helps us to understand how chemical reactions occur. 4 4 4 4 4 Chemical K Chemical K Chemical K Chemical K Chemical Kine ine ine ine inetics tics tics tics Unit 4 4 4 4 4 Chemical K Chemical K Chemical Kine ine ine inetics tics tics
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94 Chemistry that diamond is forever. Kinetic studies not only help us to determine the speed or rate of a chemical reaction but also describe the conditions by which the reaction rates can be altered. The factors such as concentration, temperature, pressure and catalyst affect the rate of a reaction. At the macroscopic level, we are interested in amounts reacted or formed and the rates of their consumption or formation. At the molecular level, the reaction mechanisms involving orientation and energy of molecules undergoing collisions, are discussed.
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This note was uploaded on 12/04/2009 for the course CHEM 120 taught by Professor Johnmichael during the Spring '09 term at Tennessee Martin.

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13654907-42 - Objectives After studying this Unit, you will...

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