7347798-chem-1571-Exp

# 7347798-chem-1571-Exp - Experiment 9 CHEMICAL KINETICS...

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Experiment # 9 CHEMICAL KINETICS Diane F. Falculan Sunshine Charisse Abadilla Chem 157.1 Prof. Yambot Department of Physical Sciences and Mathematics College of Arts and Sciences University of the Philippines Manila

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I. Introduction Chemical kinetics is a branch of physical chemistry that deals with the study of the rates of chemical reactions. It also includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that can describe the characteristics of a chemical reaction. It complements thermodynamics by supplying information about the rate of approach to equilibrium and the mechanism responsible for the conversion of reactants to products. A mathematical expression relating the rate of a reaction to the concentration of either reactants or products is called the rate law of a reaction. It tells how fast the reaction proceeds and how the reaction rate depends on the concentrations of the chemical species involved. Usually rate laws take the form, where x , y , z , are small whole numbers or simple fractions and k is called the "rate constant." The sum of x + y + z + . . . is called the "order" of the reaction. The rate equation is a differential equation and it can be integrated in order to obtain an integrated rate equation that links concentrations of reactants or products with time. There are common types of rate laws. A Zero-order reaction has a rate which is independent of the concentration of the reactant(s). Increasing the concentration of the reacting species will not speed up the rate of the reaction. Zero-order reactions are typically found when a material required for the reaction to proceed, such as a surface or a catalyst is saturated by the reactants. The rate law for a zero-order reaction is r = k, where r is the reaction rate and k is the reaction rate coefficient with units of concentration/time. A reaction is zero order if concentration data are plotted versus time and the result is a straight line. The slope of this resulting line is the negative of the zero order rate constant k. In a first order reaction, the rate is proportional to the concentration of one of the reactants. That is, v = rate = k [B], where B is a reactant. If a reaction which is known to be first order in B, such as B + other reactants → products, the rate law is written as, The constant, k , in this rate equation is the first order rate constant. A plot of ln[ A ] vs. time t gives a straight line with a slope of − k .
In a second order reaction the rate is proportional to concentration squared. For example, possible second order rate laws might be written as Rate = k [B] 2 or as Rate = k [A][B]. That is, the rate might be proportional to the square of the concentration of one of the reactants, or it might be proportional to the product of two different concentrations. However, measuring a

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7347798-chem-1571-Exp - Experiment 9 CHEMICAL KINETICS...

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