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General Chemistry Principles, Patterns, and Applications, 2011

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describing the change in reactant or product concentrations as a function of time, or as an integrated<br />

rate law, describing the actual concentrations of reactants or products as a function of time.<br />

The rate constant (k) of a rate law is a constant of proportionality between the reaction rate <strong>and</strong> the<br />

reactant concentration. The power to which a concentration is raised in a rate law indicates the reaction<br />

order, the degree to which the reaction rate depends on the concentration of a particular reactant.<br />

K E Y T A K E A W A Y S<br />

<br />

<br />

Reaction rates can be determined over particular time intervals or at a given point in<br />

time.<br />

A rate law describes the relationship between reactant rates <strong>and</strong> reactant<br />

concentrations.<br />

K E Y E QU A T I ON S<br />

general definition of rate for A → B<br />

Equation 14.4 : rate = D[ B]Dt = -D[ A]Dt<br />

Equation 14.9 : rate = k[ A]m[ B]n<br />

general form of rate law when A <strong>and</strong> B are reactants<br />

C O N C E PTUAL P R OBLEMS<br />

1. Explain why the reaction rate is generally fastest at early time intervals. For the second-order A + B → C, what<br />

would the plot of the concentration of C versus time look like during the course of the reaction?<br />

2. Explain the differences between a differential rate law <strong>and</strong> an integrated rate law. What two components do<br />

they have in common? Which form is preferred for obtaining a reaction order <strong>and</strong> a rate constant? Why?<br />

3. Diffusion-controlled reactions have rates that are determined only by the reaction rate at which two reactant<br />

molecules can diffuse together. These reactions are rapid, with second-order rate constants typically on the<br />

order of 10 10 L/(mol·s). Would you expect the reactions to be faster or slower in solvents that have a low<br />

viscosity? Why? Consider the reactions H 3 O + + OH − → 2H 2 O <strong>and</strong> H 3 O + + N(CH 3 ) 3 → H 2 O + HN(CH 3 ) + 3 in<br />

aqueous solution. Which would have the higher rate constant? Why?<br />

4. What information can you get from the reaction order? What correlation does the reaction order have with<br />

the stoichiometry of the overall equation?<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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