Molecular Kinetic Theory Model
Physics: AQA A Level, topic 6.2.6
Brownian Motion
Brownian motion was the first direct evidence of atoms.
Robert Brown
- Robert Brown noticed that tiny pollen grains suspended in still water moved about in random paths.
- The pollen would change direction without colliding with other pollen grains.
- This can be observed with a microscope for any small particles in a fluid.
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Atoms
- The random motion of the pollen grains is caused by atoms randomly colliding with pollen in the fluid.
- This is direct evidence of atoms existing.
Pressure of an Ideal Gas
The pressure of an ideal gas is closely related to the temperature and volume.
Pressure
- The pressure from a gas comes from molecules colliding with the wall of a container.
- Pressure can be increased by:
- Increasing concentration - collisions between molecules are more frequent if the molecules are packed together more tightly.
- Increasing temperature - hot gases have more kinetic energy and so more collisions will happen.
- Decreasing container size - this will increase the number of collisions.
Temperature and volume
- Pressure is linked to temperature and volume.
- Consider pumping up an empty car tire.
- Initially, the temperature will remain the same as the volume increases from a small increase in pressure.
- Next, the pressure will increase a lot as the volume refuses to expand more.
- Finally, the temperature will increase as the car is driven, this will increase the pressure.
Test yourself on Molecular Kinetic Theory Model
What was Robert Brown's evidence for atoms?
According to the kinetic theory of matter, which of the following statements is true?
When pumping up a flat tire, what initially increases quickly?
Which statements about pressure are true?
Pumping an Empty Car Tyre