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A gas is made from molecules that move in random directions & at high speeds. A gas therefore fills all parts of its container and if the container is opened, they will diffuse or spread into any available space, e.g. the atmosphere. This is how the smell of smoke travels through a room; by diffusion.

Temperature gives the particles of a gas greater kinetic energy. If the gas is not inside a sealed container, with heat, the volume of the gas expands. Therefore at the end of an experiment when a gas has been heated, you have to wait for it to cool before measuring its volume. However, if it is in a fixed space and cannot expand, its pressure increases instead. This could lead to the container exploding if the pressure becomes to great!

The air is made up of the following mixture of gases:

• Nitrogen - 78%
• Oxygen (O) - 21%
• Noble/Inert Gases - 0.5%
• Water Vapour - 0.45%
• Carbon Dioxide (CO2) - 0.05%

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