is the rate equation (and the order of reactio n with respect to each reactants) the same for all iodine rxns?

Question

I know there are different variations to iodine clock reactions but for example, will a hydrogen peroxide reaction, regardless of the concentrations of the chemicals you're using, give the same rate equation (and overall order of reaction)?

Answer 1

The order of the reaction does not change if you change the concentrations, any given reaction will always have the same order of reaction regardless. In fact, how the rate of the reaction changes over time is what defines the order of the reaction.

If changing the concentration of reagent A does not affect the rate of the reaction, then the reaction is zero order with respect to A
If the rate of the reaction is directly propotional to the concentration of A, the reaction is 1st order with respect to A (eg. doubling [A] doubles the rate of reaction)
If the rate of reaction is proportional to the square of the concentration of A, the reaction is 2nd order with respect to A (eg. doubling [A] causes the rate to increase by a factor of 4 - 2 squared)

This can be seen by plotting a graph of [A] against the rate of reaction; if the graph is a straight line the reaction is first order, if it is an exponential curve it is second order.

HOWEVER please note that, although changing the concentration of the reactants never changes the rate constant, it WILL change if you change other factors such as the temperature, or if e.g. you add a catalyst