Examples
For the reaction
The rate equation (or rate expression) is:
The rate equation does not simply reflect the reactants stoichiometric coefficients in the overall reaction: It is first order in H2, although the stoichiometric coefficient is 2 and it is second order in NO.
In chemical kinetics, the overall reaction is usually proposed to occur through a number of elementary steps. Not all of these steps affect the rate of reaction; normally it is only the slowest elementary step that affect the reaction rate. For example, in:
- (fast equilibrium)
- (slow)
- (fast)
Reactions 1 and 3 are very rapid compared to the second, so it is the slowest reaction that is reflected in the rate equation. The slow step is considered the rate determining step. The orders of the rate equation are those from the rate determining step.
Read more about this topic: Reaction Rate
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