Order of a Reaction
The order of a reaction simply refers to how many molecules are colliding together to produce a product. For instance, a reaction involving a catalyst has a reaction order of zero because the concentrations of the reactants do not figure into the rate of the reaction. Instead, the rate is governed only on how fast the catalyst works.
The thing is, reactions can go through many different steps. For instance, this might occur for the following reaction:
This is what we observe happening - A turns into B as the reaction proceeds. But, how does A turn into B? Perhaps it happens like this:
If this is really what's going on, we might say that C is dictating how much B is formed. For this reaction, only C breaks down into B. This is called a first order reaction, there only one reactant is responsible for creating the product.
What if...
But what really happens is....
In this case, A and B combine to form D . Two D molecules must come together before C can form. In this instance, this reaction is a second order reaction, because it requires two D molecules to bump into each other before product is formed.
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