chem sf 8 - Chemical Kinetics Kinetics kinetics is the...

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Chemical Kinetics
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kinetics is the study of the factors that affect the speed of a reaction and the mechanism by which a reaction proceeds. experimentally it is shown that there are 4 factors that influence the speed of a reaction: nature of the reactants, temperature, catalysts, concentration Kinetics
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Defining Rate rate is how much a quantity changes in a given period of time the speed you drive your car is a rate – the distance your car travels (miles) in a given period of time (1 hour) so the rate of your car has units of mi/hr time distance Speed =
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Defining Reaction Rate the rate of a chemical reaction is generally measured in terms of how much the concentration of a reactant decreases in a given period of time or product concentration increases for reactants, a negative sign is placed in front of the definition time [reactant] time [product] Rate time ion concentrat Rate - = = =
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Reaction Rate Changes Over Time as time goes on, the rate of a reaction generally slows down because the concentration of the reactants decreases. at some time the reaction stops, either because the reactants run out or because the system has reached equilibrium.
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Hypothetical Reaction A Product Time (sec) Number Red Numbe r Blue 0 100 0 5 84 16 10 71 29 15 59 41 20 50 50 25 42 58 30 35 65 35 30 70 40 25 75 45 21 79 50 18 82 in this reaction, one molecule of A turns into one molecule of Product the number of molecules will always total 100 the rate of the reaction can be measured as the speed of loss of Red molecules over time, or the speed of gain of Blue molecules over time
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Reaction Rate and Stoichiometry in most reactions, the coefficients of the balanced equation are not all the same H 2 ( g ) + I 2 ( g ) 2 HI ( g ) for these reactions, the change in the number of molecules of one substance is a multiple of the change in the number of molecules of another – for the above reaction, for every 1 mole of H 2 used, 1 mole of I 2 will also be used and 2 moles of HI made therefore the rate of change will be different in order to be consistent, the change in the concentration of each substance is multiplied by 1/coefficient t HI] [ 2 1 t ] I [ t ] H [ Rate 2 2 + = - = - =
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Average Rate the average rate is the change in measured concentrations in any particular time period linear approximation of a curve the larger the time interval, the more the average rate deviates from the instantaneous rate
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Instantaneous Rate the instantaneous rate is the change in concentration at any one particular time slope at one point of a curve
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chem sf 8 - Chemical Kinetics Kinetics kinetics is the...

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