0.15 Reaction rates  (Page 2/10)

The rate at which the decomposition reaction is occurring is clearly related to the rate of change of theconcentration $\left[C_{60}{O}_3\right]$ , which is proportional to the slope of the graph in . Therefore, we define the rate of this reaction as

It is clear that the slope of the graph in changes over the course of time. Correspondingly, shows that the rate of the reaction decreases as the reaction proceeds. The reaction is at first very fast but then slowsconsiderably as the reactant $C_{60}{O}_3$ is depleted.

The shape of the graph for rate versus time ( ) is very similar to the shape of the graph for concentration versus time ( ). This suggests that the rate of the reaction is related to the concentration of $C_{60}{O}_3$ at each time. Therefore, in , we plot the rate of the reaction, defined in and shown in , versus the absorbance of the $C_{60}{O}_3$ .

We find that there is a very simple proportional relationship between the rate of the reaction and theconcentration of the reactant. Therefore, we can write

As a second example of a reaction rate, we consider the dimerization reaction of butadiene gas, $C{H}_2$ = $CH$ - $CH$ = $C{H}_2$ . Two butadiene molecules can combine to form vinylcyclohexene, shownin .

provides experimental data on the gas phase concentration of butadiene $\left[C_4{H}_6\right]$ as a function of time at $T=250°C$ .