Diffusion and Changes of State Flashcards
What is diffusion?
The spreading out of particles in a gas or liquid from an area of high concentration to an area of low concentration
How can you show diffusion using bromine?
Put one gas jar containing air upside down on top of another gas jar containing bromine gas
When the lids of the gas jars are removed, the brown colour of the bromine diffuses upwards until both gas jars are uniformly brown - the bromine and air particles bounce around at random to give an even mixture
Describe the experiment to show that particles in different gases travel at different speeds?
The experiment relies on the reaction between ammonia and hydrogen chloride gases to give white solid ammonium chloride
Bits of cotton wool are soaked in concentrated ammonia solution (as a source of ammonia gas) and concentrated hydrochloric acid (as a source of hydrogen chloride gas)
These are placed in the ends of a long glass tube with rubber bungs to stop the poisonous gases escaping
A white ring of ammonium chloride forms closer to the cotton wool soaked in concentrated hydrochloric acid
Explain why the white ring of ammonium chloride forms closer to the cotton wool soaked in concentrated hydrochloric acid
Because the ammonia molecules are lighter than the hydrogen chloride molecules so they travel faster than the hydrogen chloride molecules and therefore react further away from the cotton wool soaked in ammonia solution.
Lighter particles travel faster than heavier ones
Is diffusion slower in liquids or gases?
Diffusion through a liquid is very slow if the liquid is completely still.
Liquids because the particles have less energy
How can you show diffusion in liquids?
If a small jar of strongly coloured solution (e.g. potassium manganate solution) is left to stand in a gas jar of water, it can take days for the colour to diffuse throughout the whole of the water. This is because there are only small gaps between the liquid particles for other particles to diffuse into.
Is diffusion faster at high or low temperatures?
High temperatures because the particles have more energy
Describe an experiment to show how small particles are (this seems weird and unnecessary but its on the spec)
If you dissolve 0.1g of potassium permanganate in 10cm3 of water you get a deep purple solution
Assume that the smallest drop you see is 1/1000cm3 - this means the whole solution is made from 10,000 drops. So each drop will contain 0.0001g of potassium permanganate
If you continue to dilute this by a factor of 10, you will see the colour up to the fifth dilution. If you assume you only need one particle of potassium permanganate to see the colour, the particle cannot weigh more than 0.000000001g.
In reality its smaller but this still shows how small.
What happens during melting?
When you heat a solid, the energy makes the particles vibrate faster and faster. Eventually, they vibrate fast enough so that the forces of attraction between particles are no longer strong enough to hold them together in a rigid arrangement
What happens during freezing?
If a liquid is cooled down, the particles will move more and more slowly. Eventually, the forces of attraction between them will hold them in a regular arrangement. The liquid freezes to a solid.
What happens during boiling?
When a liquid is heated strongly, the particles move fast enough to break all the forces of attraction in the liquid and the liquid boils. This happens at the boiling point.
What happens during condensing?
If you cool a gas down, the particles eventually move slowly and decrease in energy enough that attractions between them hold them in the liquid structure.
What happens during evaporation?
When a liquid changes to a gas at a temperature other than the boiling point, this is called evaporation. Not all molecules in a liquid move at the same speed. Some particles in the liquid are moving faster than average and these may have enough energy to break away from the surface of the liquid to form a gas.
What happens during sublimation?
When a solid turns directly into a gas. When a gas turn directly into a solid this is usually called reverse sublimation.
