Chapter 55: Problem 12

Comment on the appropriateness of the following methods to determine the order of a reaction. i) Examine the stoichiometric coefficients in the chemical equation. In this method, the order of a reaction with respect to a component is equal to the stoichiometric coefficient of that component in the chemical equation. ii) Perform experiments. In this method, the order of a reaction with respect to a component is determined by how the reaction rate changes when the concentration(s) is changed.

Short Answer

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The appropriateness of the two methods depends on the situation. Stoichiometric coefficients ('Method 1') might initially suggest a reaction order but don't definitively confirm it. Preferred method is experimentally determining the reaction order ('Method 2'), because it aligns with how reaction order is defined - by how reaction rates change with concentrations of reactants.

Step by step solution

Analyzing Method 1

Method 1 suggests that the order of a reaction with respect to a component equals the stoichiometric coefficient of that component. However, while this seems straightforward, it is not generally valid. Stoichiometric coefficients offer information about the balanced chemical equation but do not directly map to the reaction order. This is because reaction order is determined by the reaction mechanism (the step-by-step molecular level view) which doesn't necessarily correlate with the overall balanced equation.

Analyzing Method 2

Method 2 entails carrying out experiments to observe how the reaction rate varies with changes in concentration. This method is often more reliable because the order of a reaction is defined by how the rate of reaction responds to changes in concentrations of reactants. By comparing the rate of the reaction under different concentrations, one can define the order of the reaction with respect to each reactant. This method often includes rate law determination, time-concentration studies or isolation method.

Summary of Appropriateness

Upon analysis, it becomes clear that the appropriateness of these methods largely depends on the situation. Using stoichiometric coefficients can offer an initial suggestion for reaction order, but it's not universally applicable because the reaction order depends on the reaction mechanism, not just stoichiometric coefficients. Method 2 - performing experiments - tends to be more reliable and is generally the preferred method for determining reaction order because it traces how the reaction order responds to changes in reactant concentrations, which is the elemental definition of reaction order.

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Short Answer

Step by step solution

Analyzing Method 1

Analyzing Method 2

Summary of Appropriateness

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