GCSE Physics (AQA)

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Demonstrating Gas Pressure

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Particle model of matter Particle model and pressure

Demonstrating Gas Pressure

2:20 Gas Pressure and Kinetic Theory
Spec 4.3.3.1
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  • Gas pressure is demonstrated by heating a liquid in a sealed tin.
  • Pressure from a gas is caused by collisions between particles and the walls of the container.
  • The experiment is dangerous and should not be done at home.
  • First step: pour a small amount of water into a tin and seal it with a close-fitting lid.
  • The container should be made of metal or another strong material.
  • Gas particles inside the tin exert the same outward force as the inward force exerted by particles outside the tin.
  • There is an outward pressure on the tin due to collisions from air molecules inside and an inward pressure from air molecules outside.
  • Overall, no effect is noticed from these pressures as they are equal and opposite.
  • Step three: gently heat the water using a bunsen burner.
  • Thermal energy is transferred from the bunsen burner to the water and air inside the container, heating them.
  • Water will evaporate and release more gas particles into the tin, reaching boiling point and turning to steam.
  • Gas particles move faster as their temperature increases, gaining kinetic energy from heat flow.
  • Step six: outward pressure from the gas becomes greater than the inward pressure, causing the lid to fly off.
  • The lid is the weakest part of the tin, resulting in it being pushed off by the outward force.
  • It is important to wear eye protection and keep a distance when observing this experiment.

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