Hello Everyone, welcome back to another written lecture on Teach Me to Science where I dump all of the information I've acquired about general chemistry into a single page. Today, I'm going to recall everything I can about a general chemistry topic called Collision Theory.
Why you should understand Collision Theory:
Collision Theory is a fundamental theory that explains how chemical reactions occur. There are several key components to this theory, all of which explain how chemical reactions occur and what factors limit chemical reactions.
Key Ideas
- Collision Theory Definition
- Orientation
- Temperature or Energy
- Molecularity and Reaction Steps
Collision Theory Definition
Collision Theory describes the requirements for a reaction to occur. If the specific requirements aren't met, no reaction will happen.
The key requirements for a reaction to occur are...
1. Orientation
2. Energy
3. Molecularity
I will be describing each of the requirements in detail in the below segments of this post. Ultimately, if each of the requirements are not, met no reaction will occur.
Orientation
For a reaction to occur successfully, the molecules must collide in the correct orientation.
If the reaction occurs between a hydrogen and a oxygen but the molecules collide in such a way that the hydrogen and oxygen are nowhere near each other, then the reaction will not occur.
The image to the left shows two different reaction scenarios.
The left side shows a collision occurring between the two central atoms of the molecule. This collision doesn't result in a reaction. Instead, the molecules bounce off each other and continue on their way.
The right side shows a collision occurring between a central atom and a peripheral atom. This collision results in a reaction where a bond forms between the two central atoms and the peripheral atom is kicked off. Only when these to molecules collide in this way does a reaction occur.
Temperature or Energy
Another key requirement is that the collision described above must occur with enough energy.
If the molecules collide in the correct orientation but do not have enough energy, no reaction will occur. Energy can be stored within the molecules as vibrations within the bonds, or an increase in temperature can cause the molecules to bounce around their container faster. Increasing temperature increases the speed of the molecules in the container and the energy each molecule has.
Increasing temperature is one-way chemists make a reaction occur more quickly. A reaction will be more likely to occur at a higher temperature because of the increased amount of energy each molecule has. This increased energy will increase the likelihood that two molecules collide with enough energy for a reaction to occur.
Molecularity and Reaction Steps
Molecularity is the number of molecules that must collide for a reaction to occur. The more molecules which must collide with each other, the less likely a reaction is to successfully occur. Consider the question below.
Increasing the number of molecules which must collide makes a reaction less likely to occur. How do reactions which require 4, 5, or even 6 molecules to collide, occur successfully? The answer is Reaction Steps.
Reactions occur in steps because a series of reactions which are broken down into numerous but simpler steps are more likely to occur.
Remember: everything in chemistry is about stability. In the simplest terms, chemistry is a quest for stability. Reactions occur because they result in a product that is more stable. Breaking a reaction down into steps creates intermediates which are more stable. If a reaction step involves more than 3 molecules reacting, it is very unlikely to occur.
The number of reactants, or the molecularity of a reaction, significantly impacts if the reaction will occur successfully. Therefore, it is a key component of collision theory.
Summary
- For a reaction to occur successfully, the molecules must collide in the correct orientation.
- The collision described must occur with enough energy. Increasing temperature increases the speed of the molecules in the container and the energy each molecule has.
- Molecularity is the number of molecules that must collide for a reaction to occur.
- Breaking a reaction down into steps creates intermediates which are more stable. If a reaction step involves more than 3 molecules reacting, it is very unlikely to occur.
I hope you have found this post on collision theory helpful. If you have any questions or would like clarification on a topic, feel free to comment on this post or message me through my website.
Likewise, you can also comment on the youtube video version of this post. I've attached the link to it below.
- Saren
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