Reaction Rates and Collision Theory
Reaction rates and collision theory
It should be clear now that the average rate of a reaction varies depending on a number of factors. But how can we explain why reactions take place at different speeds under different conditions? Collision theory is used to explain the rate of a reaction.
For a reaction to occur, the particles that are reacting must collide with one another. Only a fraction of all the collisions that take place actually cause a chemical change. These are called successful or effective collisions.
Definition: Collision theory
Collision theory explains how chemical reactions occur and why reaction rates differ for different reactions. It states that for a reaction to occur the reactant particles must:
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collide
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have enough energy
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have the right orientation at the moment of impact
These successful collisions are necessary to break the existing bonds (in the reactants) and form new bonds (in the products).
Optional Activity: Collision Theory
Aim
To determine the best way to approach your friend, in order to link your right arm with their left arm.
Method
Try different ways of approaching your friend:
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back to back
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front to back
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side to front
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side to side
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front to front
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etc
Results
Determine how hard it is to link arms in each of these positions.
Discussion
If you approach your friend from behind (facing their back) it is hard to link arms. Approaching from their left (sideways so that your right side is on their left), it is easy to link up.
Conclusion
You should have found that each method had a different level of difficulty for linking arms. This is similar to how molecules (compounds) approach in a reaction. The different ways you approached your friend represent the different orientations of the molecules. The correct orientation makes successful collisions possible.
This lesson is part of:
Energy and Chemical Reactions