Random collisions.?

Question

if all collisions in a chemical reaction are random,consider the following situation:
A+B---->C+D.
if this reaction is taking place in a closed system,there is a probability that A's random motion might be such that it doesnot encounter the molecules of B at all.So can we say that no chemical reaction is a certainity?

Answer 1

We cannot say that. In order for A and B to never react then they must never collide with the proper orientation and with the proper energy. Suppose those types of collisions are very rare so that the probability of one occuring is only one collison out of every million (this is a probability of 1/1,000,000). Since there are only two types of collisions to wory about (reactive collisions and unreactive collisions) then everytime A collides its chances of not reacting are nine hundred ninty-nine thousand nine hundred ninty-nine out of one million or a probability of not reacting equal to 999,999/1,000,000 (this is just one minus the probability of having a reactive collisoin).

Now, in order for A to never react then every single time it collides it must have a unreactive collision. The probability of not reacting on its first collision is 999,999/1,000,000. The probability of this happening two times in a row is the probability of it happening once multiplied by the probability of it happening again or (999,999/1,000,000)(999,999/1,000,000) which is the same as, (999,999/1,000,000)^2. The probability not reacting three times in a row would therefore be (999,999/1,000,000)^3. The probability not reacting four times in a row would be (999,999/1,000,000)^4 etc.

Since the probability of A not reacting upon colision is less than one then everytime we raise the power the result gets smaller and smaller. So while there is a good chance that A will not react on its first collision, its chances of surviving one billion collisions is essentially zero, and the longer the reaction mixture sits the more certian we can be that a reaction will take place.

Answer 2

There is no such thing as a reaction that does not occor, that is against the principle of microscopic reversibility. It is all statistics. A and B will react, even if the liklihood makes it occur once every billion-billion years (of course this is practically considered a non-reaction). All reactions occur, its just a matter of how patient the experimenter is.

It is also impossible to say that A and B will not encounter eachother, that is completely random and based on their specific populations, it is a matter of them being in the right orientation when they encounter eachother that they react. If the activation barrier is high to getting into that orientation then the odds of a reaction to C + D does not occur easily.

The reaction of alkenes with chlorine occurs very quickly in the presence of light because the energy to overcome the energy barrier is exceeded....however, statistically the system can go over that barrier thermally eventually.

Answer 3

Yes, you could say that. All chemical reactions cannot happen spontaneously. Sometimes the molecules do not have enough internal energy to overcome the activation energy barrier for the reaction, even if they collide within closed containers. This is why certain reactions, like the halogenation of alkanes, require the presence of light in order for the reactants to gain the kinetic energy needed for the reaction to occur. Other factors which affect are thermodynamic stability(energy state) of the reactants and perhaps the collision theory too.

If the reaction between A and B fits in that category, then 'no chemical reaction' is indeed a certainty, but in normal conditions.

Answer 4

It's true that we can't say for certain that a chemical reaction is going to occur. But the probability of chemical reaction happening is anywhere between 0% and 100%. So, even though we are not sure a chemical reaction will occur or will not, there is probability that the chemical reaction will. The probability of reaction occurring depends on many other factors such as temperature, pressure, reacting chemicals, etc.

Answer 5

If you had a cubic container one meter on a side, and you put one molecule of A and one molecule of B in that box, then the chance of the two molecules meeting and reacting would be infinitesimally small.

However, when you are talking about reactions, you are talking moles of substance in that 1m^3 box. Recall that a mole is 6.023x10^23 units of a substance, so if we have a mole of A and a mole of B, that's a BUNCH of As and Bs flying around in that box. When talking in those kinds of numbers, the probabilities of collisions occurring jump WAY up.

Then, of course, we have to have enough energy to ensure that the collisions would be capable of completing the reaction (activation energy) by overcoming the electrostatic repulsions of the electron shells around the atoms that make up A and B.

Answer 6

No. All you can say is that no reaction is a possibility. Some reactions go to completion (which means that every A reacted), but some don't (which means that either some A did not react or you have an equilibrium - the A reacted to form product, then reacted back to form A).

Answer 7

You can say that no chemical reaction is a POSSIBILITY, not a certainty. It is not a certainty that A will never encounter B, so therefore, it is not a certainty that no chemical reaction will occur.

I think you need to look over your question because the English and word usage is pretty sketchy.

Answer 8

One can say that there is no certainty that the reaction will occur at that specific moment. However, the chances of the reaction never occuring is very minimal.

Answer 9

there is the probability factor of course