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Collision Theory - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Collision theory is a model for explaining chemical reactions and reaction rates using the interactions of particles within the reactants. There are three important parts to collision theory, that reacting substances must collide, that they must collide with enough energy and that they must collide with the correct orientation. Increasing the kinetic energy of these particles or decreasing their volume increases the frequency of collisions and speeds a reaction.

Alright so we're going to talk about the collision theory. And the collision theory comes into play when you're talking about reactions and actually what happens in a reaction and how a reaction actually goes from the reactant all the way to the product. So the first thing we're going to have to discuss is, the fact that the reacting substances whatever we're dealing with the atoms, ions or molecules must collide in order for the reaction to occur. Okay that seems pretty obvious so we have our 2 reactants a and b and they must collide, and this is what we're going to call activated complex or a transition states that's going from, transitioning from the reactants towards the product and it's going to recreate this independent, very high energy activated complex and then yield our products, our 2ab. So the first postulate is that they must come together, okay that's easy enough.

The second one says the reactant substances must collide with sufficient energy in order to form that activated complex. Because this activated complex is extremely high, very high in energy, very unstable so they must collide with a certain amount of energy to get to this point. If they don't collide with a good amount of energy then they're actually not going to react at all. So that energy is going to be called our activation energy to get to our activated complex. And you might see the symbol e with a subscript a to note that. And the last thing in the collision theory is that reacting substances must collide with the correct orientation so if they, made a collision at a range that wasn't great for them, they would actually rebound off of each other and not react at all.

But if they if they did they have to make sure they line up correctly and then for the correct reaction to occur then they get their activated complex to form the products. And so these 3 things are the basis of that collision theory and how reactants go from reactants to the products.