Chapter_14-Kinetics

Chapter_14-Kinetics - Ch.14.Kinetics Chemical kinetics The...

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Chemical kinetics Ch.14.Kinetics - This is a well formalized branch of chemistry. - Those who are familiar with elementary mathematics must have no difficulties in understanding the chemical kinetics. The term derives from the Greek word κίνησις (kinesis) meaning “movement”.
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What is a reaction rate Ch.14.Kinetics Considering the simplest irreversible reaction A B Definition: Reaction rate is the change in the concentration of reactants or products per unit of time Rate = Molarity change / time change; Unit: M /s=mol/(L s)
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Average rate and instantaneous rate Ch.14.Kinetics Rate = ([A] 2 -[A] 1 ) / (t 2 -t 1 ) = - A/ t Rate can change with time Tangent line touches the curve in a single point.
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Reaction rates and stoichiometry Ch.14.Kinetics In general case of a reaction a A + b B c C + d D (In other words, the reaction rate is the rate of disappearance of the reactants and the rate of appearance of a product) t D d t C c t B b t A a Rate = = - = - = ] [ 1 ] [ 1 ] [ 1 ] [ 1
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Using spectroscopy to measure reaction rates Ch.14.Kinetics The wavelength is tuned according to a reactant or a product of interest Bouguer-Lambert-Beer’s law A = a b c Light absorbance Molar absorptivity constant Path length Molar concentration
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Factors affecting the reaction rate Ch.14.Kinetics 1.The physical state of the reactants 2.The concentration of the reactants 3.The temperature at which the reaction occurs 4.The presence of a catalyst
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Concentration and the reaction rate Ch.14.Kinetics In general case of a reaction a A + b B c C + d D Rate = k [A] m [B] n Reaction order in the reactant A Reaction order in the reactant B Overall reaction order = sum of orders in all reactants. Reaction orders usually are small numbers, 0, 1 or 2. They can be fractional. Rate constant Rate law:
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the reaction rate Ch.14.Kinetics 2N 2 O 5 (g) 4NO 2 (g) + O 2 (g) Rate = k [N 2 O 5 ] (reaction order = 1) CHCl 3 (g) + Cl 2 (g) CCl 4 (g) + HCl(g) Rate = k [CHCl 3 ] [Cl 2 ] 1/2 (reaction order = 1.5) H 2 (g) + I 2 (g) 2HI(g) Rate = k [H 2 ] [I 2 ] (reaction order = 2) In general case a reaction orders must be determined experimentally – using initial concentrations of reactants.
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This note was uploaded on 01/02/2012 for the course CHEM 114 taught by Professor Sergeiaksyonov during the Fall '11 term at ASU.

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Chapter_14-Kinetics - Ch.14.Kinetics Chemical kinetics The...

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