|Kinetics : Order and Molecularity|
Molecularity - The number of molecules consumed in a chemical reaction
Step 1: N2O5 NO2 + NO3
Step 2: NO2 + NO3 NO2 + NO + O2
Step 3: NO + NO3 2 NO2Unimolecular - When a single molecules is consumed. e.g. Step 1 in the above reaction.Order - Describes the relationship between the rate of a step in a chemical reaction and the concentration of one of the reactants consumed in that step.
Bimolecular - When two molecules are consumed. e.g. Steps 2 and 3 in the above reaction.
First-Order - The rate of the reaction depends on the concentration of a reactant raised to the first power.
The #1 for the first power is usually omitted because any number raised to the first power equals itself.
Rate = k[N2O5]
The above reaction is first order with respect to [N2O5] and first order overall.
The rate of the overall reaction is the sum of the orders of all the reactants
If there is only one reactant, then the order with respect to that reactant is equal to the order of the overall reaction.
The above reaction is second order with respect to [HI] and second order overall.
Rate = [NO]2[O2]
The above reaction is first order with respect to [O2] and
second order with respect to [NO].
The overall reaction is third order, or higher order.
The above reaction is mixed order with respect to [NO] and higher order with respect to [Cl2]3.