02.06.2013 Views

Untitled - Kelly Walsh High School

Untitled - Kelly Walsh High School

Untitled - Kelly Walsh High School

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

200 CHEMISTRY FOR THE UTTERLY CONFUSED<br />

The latter method is usually preferable, and we shall employ it in this example.<br />

When we rearrange the equation to find the rate constant, k, and enter the appropriate<br />

values:<br />

k <br />

We will now examine a problem that is not first order. Molecules of butadiene<br />

(C 4H 6) will dimerize to C 8H 12. The rate law is second order in butadiene, and the<br />

rate constant is 0.014 L/mols. How many seconds will it take for the concentration<br />

of butadiene to drop from 0.010 M to 0.0010 M?<br />

This is a second-order reaction. The following relationships apply to first order<br />

reactions:<br />

These are the only equations we have exclusive to second-order reactions. For<br />

this reason, one or more of these equations will be necessary to work the problem.<br />

(In this problem, A is butadiene.)<br />

Using the list of terms ([A] 0, [A] t, k, t, and t1/2), and the given information, we<br />

find that k 0.014 L/mols, [A] 0 0.010 M, [A] t 0.0010 M, and t ? s The<br />

1<br />

only second-order relationship with these four terms is: . We<br />

1<br />

kt<br />

can rearrange this relationship to isolate the time and enter the given values:<br />

t <br />

ln [A] 0<br />

[A] t<br />

t<br />

1<br />

[A] t<br />

<br />

Rate k[A] 2<br />

1<br />

[A] 0<br />

<br />

k<br />

ln [1.000]<br />

[0.355] 1.035637<br />

0.243679 0.244 min1<br />

4.25 min 4.25 min<br />

1 1<br />

<br />

[0.010] 0<br />

<br />

0.014 L/mol·s<br />

[0.0010] t<br />

(900)<br />

0.014 s 1 64285.7 6.4 10 4 s<br />

1<br />

<br />

[A] t<br />

1<br />

kt t1/2 <br />

[A] 0<br />

1<br />

k[A] 0<br />

(1000 100) L/mol<br />

0.014 L/mol·s<br />

Kinetics is the study of the speed of reactions. The speed of reaction is affected<br />

by the nature of the reactants, the temperature, the concentration of reactants,<br />

the physical state of the reactants, and catalysts. A rate law relates the speed of<br />

reaction to the reactant concentrations and the orders of reaction. Integrated<br />

rate laws relate the rate of reaction to a change in reactant or product concentration<br />

over time. We may use the Arrhenius equation to calculate the activation<br />

[A] t<br />

[A] 0

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!