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Elements, Compounds and Mixtures

What is Diffusion?

Diffusion is the random movement of one liquid or gas
through another, from a region
of high concentration to a region of low concentration.


Why is Diffusion of a Gas through Air Slow?

When two gases mix together, the fast randomly moving
particles collide, and this slows down their rate of mixing.
Examples are the diffusion of bromine through air and
the diffusion of hydrogen chloride and ammonia through air.


The Diffusion of Bromine through Air.

Bromine is a red-brown liquid that boils at 58 °C.
Bromine gas is also red-brown and can be seen inside a gas jar.

If bromine gas is allowed to enter a gas jar containing a vacuum,
the red-brown colour instantly fills the jar
because there are no air molecules to collide with.
This shows that the bromine molecules are moving very fast.

When bromine is added to a gas jar filled with air,
the red-brown gas is seen to slowly diffuse through the air.
The many collisions between the bromine molecules
and the air molecules slow down the rate
at which the red-brown bromine gas fills the jar.

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