DP Study Guide for Chaper 13

DP Study Guide for Chaper 13 - DP's Study Guide for Chapter...

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DP’s Study Guide for Chapter 13 General Chemistry, 4th Ed.”, Hill, Petrucci, McCreary, and Perry (ISBN 0-13- 140313-3) This is about how fast reactions occur. Up to this point you are only suppose to know that things react. “Scene 1” is reactants, and some time later you look again at “Scene 2” where products are now present and left over reactants are viewed. This chapter you get to watch the whole process unfold. 13.1 Chemical Kinetics: The speed or rate of a reaction can be monitored by observing the rate of disappearance of the reactants or the rate of formation of products. This rate is not a constant through-out the reaction. Rates are concentration dependent so the reactant pile disappears very quickly in the initial stages of the reaction, and slows down near the end when the amounts of the reactants are less. This concentration dependence is a big part of this chapter. Other factors are the temperature, available surface area, and the presence of catalysts. First we do concentration. 13.2 The Meaning of Reaction Rates: In liquids we measure the concentration at two different times. The reaction rate is C/ t, the units will be M/s (molarity, big M). Rates of reaction are stoichiometrically related, by equation 13.1. Reactant rates are negative because the concentration falls, products have positive rate because their concentrations are increasing. Learn how disappearance and appearance rates for products and reactants by relating them through the stoichiometric fractors. Exercise 13.1B Problems: 25, 26 13.3 Measuring Reaction Rates: There are three kinds of rate measurements, initial rates, instantaneous rates, and average rates. The difference between the three is shown in figure 13.5 where the concentration is plotted as a function of time. I practice initial rates are the only ones determined. You do not have to wait so long. Problems: 24, 75 13.4 The Rate Law of a chemical reaction: The most popular method to measure the speed of a reaction is the “method of initial rates”. It also gets the experiments over quicker. The effect concentration has on the rate of the reaction is given by the rate law which has the form R = k[A] m [B] n the exponents m and n can only be determined experimentally. The sum of all the exponents is called the order of the reaction. k is the rate constant and unlike R it is independent of concentrations. The exponents are discovered by doing a series of experiments in which only one of the concentrations of the reactants is varied. If m = 1, then you say the rate is first order in compound A. If you double the concentration of A, holding B constant, you expect the rate to double. You double B concentration and the rate goes up by a factor of 4 then n = 2. Two
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squared is four, right? Works some problems where you are given initial rate data. Problems: 30, 31,32, 35, 36, 48, 93
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DP Study Guide for Chaper 13 - DP's Study Guide for Chapter...

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