In
an example discussed earlier we saw that the reaction of NO with H2
leads to a rate
expression that is different from what might be expected from
the equation of the reaction alone:
The reaction is first order in H2 concentration, not second order. One mechanism that will account for this rate behavior is
This mechanism is illustrated in fig 7 opposite. If all reactions except the k3 process are quite fast, then the rate equation is
The last reaction (k4)
occurs so fast that it scavenges any N20
as rapidly as it is formed, and has no effect on the overall rate
of the process. In effect, N2 is produced
as fast as N20 appears, so
In a series of reactions, the slowest one has the greatest influence on reaction rates. To invoke a painful analogy, if it takes ten days to to get a certified letter from Los Angeles to the White House, then rushing to get it into the one o'clock mail instead of the three o'clock will make little difference in the long run. |
