Kinetics: Collision Theory, Maxwell-Boltzmann Distribution
This part of your AQA AS Chemistry exam is mega-easy! Very easy marks are to be had, so long as you memorize what’s below!
Collision Theory
- For a reaction to occur
- particles must collide
- with enough energy
- Not all collisions are successful, because not all particles have the activation energy
- The activation energy is the minimum energy required for a reaction to occur
The Maxwell-Boltzmann Distribution
- In a sample gas or liquid, the molecules are flying about and bumping into each other and the walls all the time.
- When they do this, no energy is lost from the system - they’re elastic collisions.
- So in a sample of gas or liquid at any given time, the energy each molecule has is going to be spread out, with some particles having more or less energy than others.
- If you were to draw a graph of how the energy was spread over different molecules, you’d get the Maxwell-Boltzmann distribution!
This graph is mega-important if you want to get those easy marks. You have to remember that:
- the area under the curve = the total molecules in the sample, and doesn’t change
- there are no molecules with no energy
- very few molecules have high energies, but
- there is no maximum energy for a molecule, and
- the most probably energy value is where the curve is at it’s highest, as shown.
If you increase the temperature of the sample, the distribution changes as show below. It becomes stretched out and has a lower peak, but the area under the curve remains the same.
The reverse happens when you cool down a sample.