Wednesday, December 2, 2009

Kinetic Theory igcse/gcse/ olevel chemistry notes

Kinetic Theory
Three states of matter – solids, liquids and gases.
Matter made up of very small particles in constant motion.
In solids the particles are packed very close together. They vibrate about fixed positions and have strong forces of attraction between them.
Solids :
have a high density
can not be compressed
do not flow
have a fixed shape
have a fixed size

In liquids the particles are close together but not as close as they are in solids. They can move around in any direction and are not fixed in position. The forces of attraction between them are still quite strong but, again, not as strong as in solids.
Liquids :
have a medium density
can not be compressed
can flow
have the shape of their container
have a fixed size

In gases the particles are very far apart with large distances between them. They move around very quickly in all directions and the forces of attraction between them are very, very weak.
Gases :
have a very low density
can be compressed
can flow
have the shape of their container
have the size of their container

You can change the state of a substance by heating or cooling it.

When the change is from a solid to a liquid it is called melting.
When the change is from a liquid to a gas it is called evaporating.
When the change is from a liquid to a solid it is called freezing.
When the change is from a gas to a liquid it is called condensing.
When a solid is heated it changes to a liquid and then a gas. A graph of temperature against time for this process would look like this:

KEY
A:
Over portion A the particles in the solid are vibrating more and more as they gain the heat energy so the temperature rises.
B:
Over portion B, as the solid changes into a liquid, all the energy is being used to overcome the strong forces of attraction between the particles and separate them so the temperature does not rise
C:
Over portion C the particles move around faster as they gain energy so the temperature rises.
D:
Over portion D the heat energy is all being used to separate the particles and overcome the forces of attraction between them so again the temperature does not rise as the liquid changes to a gas
E:
Over part E the temp rises as the particles move around faster

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