You do indeed make sense. It is interesting to follow your thoughts. First point is that when you have a reversible reaction,
k
1A
Z
k
-1that the reaction proceeds until equilibrium is reached. In that case the equilibrium constant is related to the forward and reverse rate constants:
K
equil = [Z]
equil/[A]
equil = k
1/k
-1If you use this, and plug in Arrhenius and any transition state theory quantities like entropy, internal energy, etc, most of what you are saying will make sense.
When you are discussing mechanisms, like collision cross sections, steric factors, then you are talking about the end goal of chemical kinetics: that is you what to know the steps that lead from reactants to products. Now we can usually come up with a "reasonable" mechanism that is consistent with the rate law, but this consistency does not mean that the mechanism is correct.
But mechanisms are great to visualize steps.
It might help to look at chemical kinetics in the following way.
What is the real objective in understanding chemical changes? You want to know how the particles react. That information must be in the empirical rate equation obtained from experiments.
So let us consider that rate equation and take it apart. First we find the way the data plots to give us the orders of the reaction. Usually pretty easily done. So with that we can remove the concentration dependencies from our empirical rate law. Less stuff to worry about.
Now we are left with the rate constant, k. We study it and find that under different conditions, rates can change. Hence the rate constant can be temperature, pressure and field (electric, magnetic) dependent. Let's just use temperature. Then Arrhenius found the exponential relation that allows us to separate out the dominant temperature dependence of the rate constant, leaving us with the Pre-exponential factor. That is where the interest lies.
First you might ask why in Arrhenius you find the ratio of the activation energy to RT,
k = A exp(-E
a/RT)
How RT is called the "thermal energy" which simply means it is the heat available around us. For us it is RT= 8.314 X 300 = 25 kJ/mol . Go out in space and it is 3 K or go to the sun and it is 6000 K. This energy that surrounds us is available for use in processes. So getting over a higher activation energy barrier is easier the more the thermal energy increases.
I am rambling, but we are here on Earth because our thermal energy is such that stable chemical bonds can occur. Not many chemical bonds on the sun, and not enough energy in outer space to mount any activation energy. So we are lucky to have our Earth.
So finally the pre-exponential factor is what is left over after removing temperature, activation energy and concentration from the empirical rate equation. That is where we learn about the mechanisms, find out what collisions might do, and learn about intermolecular forces.
BTW the entropy comes in at the pre-exponential level too, and really formalizes the more empirical steric factor. Non-the-less calculations including collisions we can actually do, like hard spheres, give remarkable insight into what is going on.