Effect of Concentration on Reaction Rates The Rate Law

One of the goals in a chemical kinetics study is to derive an equation that can be used to predict the relationship between the rate of reaction and the concentrations of reactants. Such an experimentally determined equation is called a rate law, or rate equation. 

The terms [A], [B]. represent reactant molarities. The required exponents, are generally small, positive whole numbers, although in some cases 

The term order is related to the exponents in the rate law and is used in two ways (1) If m = 1, we say that the reaction is first order in A. If n = 2, the reaction is second order in B, and so on. (2) The overall order of reaction is the sum of all the exponents m + n + -. The proportionality constant k relates the rate of reaction to reactant concentrations and is called the rate constant of the reaction. Its value depends on the specific reaction, the presence of a catalyst (if any), and the temperature. The larger the value ofk, the faster a reaction goes. The order of the reaction establishes the general form of the rate law and the appropriate units of k (that is, depending on the values of the exponents). With the rate law for a reaction, we can 

But how do we establish the rate law We need to use experimental data of the type described in Sechon 20-2. The method we describe next works especially well. 

As its name implies, this method requires us to work with initial rates of reaction. As an example, let s look at a specific reaction that between mercury(II) chloride and oxalate ion. 

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Effect of Concentration on Reaction Rates The Rate Law—The relationship between the rate of a reaction and the concentrations of the reactants is called the rate law (rate equation) (equation 20.6) it has the form rate of reaction = fc[A] [B] . The order of a reaction refers to the exponents in the rate law. If... 

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