[Elmorshedy]

Suppose in the reaction 2 NO + O2 --------> 2NO2

Why when the the concentration of NO is doubled, the rate increases 4 times, I know that the rate is directly proportional to the square of NO concentration (I don't know why) and it's order of reaction is 2 ( I don't why ). but I still can't understand a reason for all of that it seems foggy to me why the coefficient affects the proportionality. It should be intuitive to a chemistry student, but to me and to a lot of students it's intuitive that when the concentration doubles the rate doubles no matter its Coefficient, I mean why does the number of moles in a balanced question affects the proportionality in the rate equation for an example 2NO + O2  2NO2 , I2 + H2  2HI

Supposing that they are elementary reactions
Why in the first equation on doubling the concentration of NO the rate increases 4 times but on doubling I2 it increases only 2 times

I already know the conception of the order of reaction and this stuff

but I want an analogy that really clarifies it, or a detailed easy explanation that make it clear and intuitive to a high school student.

Another form of my question why is the concentration raised to a power that equals its coefficient in the reaction rate equation

[sandwich4]

Firstly if rate is proportional to ([NO])², then rate = k x ([NO])². Doubling the concentration of NO would give rate = k x (2 x [NO])² = k x 2² x ([NO])² = k x 4 x ([NO])². So the rate increase four fold.

If the reactions aren't elementary then the coefficients usually mean nothing to the order of reaction or orders with respect to species. If the reactions are elementary, i.e. occur as a single step, then the coefficients of the species represents the order with respect to that species.

For an explanation, say 2A + B  C was an elementary reaction then doubling the concentration of B can make the two molecules of A twice as likely to find a B molecule. However doubling the concentration of A makes it twice as likely that B would find the first molecule of A to react with, but also twice as likely to find the second molecule of A, so a molecule of B is four times more likely to find the two A's it's looking for.

[Elmorshedy]

.

For an explanation, say 2A + B  C was an elementary reaction then doubling the concentration of B can make the two molecules of A twice as likely to find a B molecule. However doubling the concentration of A makes it twice as likely that B would find the first molecule of A to react with, but also twice as likely to find the second molecule of A, so a molecule of B is four times more likely to find the two A's it's looking for.

It

 became clearer thaks to you, but how does that reaction occurr
 2A + B    C should 2 A molecules collide with one B molecule or with each A molecule there's a B which collides then reaction occurs?

[sandwich4]

Well it was a bit hypothetical because you don't really get three molecules which collide at the same time because this is too unlikely, so only two species can collide at once. But A + B AB then AB + A C could work, or two B molecules then an A.