Effect of Concentration on Rate

The concentration of the reaction components determines the rate of reaction. For instance, for the irreversible reaction 

As indicated above, the dependence of rate on concentration can be shown to be of the general form 

For elementary reactions, the law of mass action states that the rate is proportional to the concentrations of the reactants raised to the power of tneir respective molecularity. Thus for an elementary irreversible reaction such as (7-4) the rate equation is 

the exponents p and q of Eq. (7-7) are the stoichiometric coefficients when the stoichiometric equation truly represents the mechanism of reaction, i.e., when the reactions are elementary. As discussed above, the exponents a and b in Eq. (7-5) identify the order of the reaction, while the stoichiometric coefficients p and q in Eq. (7-7) also identify the molecularity—for elementary reactions these are the same. 

The Arrhenius equation relates the specific rate constant to the absolute temperature 

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In this discussion, we generally consider reactions for which the products do not appear in the rate law. In these cases, the reaction rate depends only on reactant concentrations and temperature. First, we look at the effect of concentration on rate for reactions occurring at a fixed temperature. For a general reaction,... 

We then show that the effect of concentration on rate is expressed quantitatively by rate laws and show how rate laws and rate constants are determined experimentally. 

EXERCISE 14.4 Relating a Rate Law to the Effect of Concentration on Rate... 

A reaction is the result of a colHsion between reactants, and therefore, it makes sense that increasing the concentrations of reactants should increase the frequency of collisions that lead to a reaction, thereby increasing the rate of the reaction. However, the precise effect of concentration on rate must be determined experimentally ... 

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