The Three States of Matter
The three states, SOLID, LIQUID and GAS are called the three states of matter (see Kinetic Theory)
The boiling point of a substance is the temperature that causes it to change from a liquid to a gas
At a temperature ABOVE its boiling point a substance will always be a gas
The melting point of a substance is the temperature that causes it to change from a solid to a liquid
At a temperature below its melting point a substance will always be a solid
At a temperature between its melting point and boiling point it will be a liquid
eg
| Substance | Melting point | Boiling point | State at room temperature |
| Water | 0° C | 100° C | Liquid |
| Lead | 327 | 1740 | Solid |
| Mercury | -39 C | 357 C | Liquid |
| Oxygen | -218 | -183 | Gas |
You don’t need to remember the melting points and boiling points but you DO need to know why each substance is a solid, liquid or gas.
You DO need to know the melting point and boiling point of water
Water:
Boiling point of water = 100° C
Melting point of water = 0° C
A substance can be made to change state by making it hotter or colder
getting hotter:
MELT : When a solid turns to a liquid. This happen as soon as the substance reaches (or goes above) a temperature called its melting point
eg WAX melts when heated.
EVAPORATE: When a liquid turns to a vapour
BOIL: This is when a liquid turns to a vapour at its boiling point.
eg WATER boils when heated.
SUBLIME This is when a solid turns to a vapour without becoming a liquid
eg IODINE turns from a solid to a purple vapour when heated
Getting colder
CONDENSE: This is when a vapour turns to a liquid when it is cooled down (to below the boiling point)
FREEZE (or solidifying): This is when a liquid turns to a solid. This happens when the liquid cools to below its melting point.
SUBLIME This is when a vapour turns to a solid without becoming a liquid
eg IODINE turns from a purple vapour to a black solid when heated
[notice that the same word (subliming) is used for the change from a solid to a vapour and from a vapour to a solid]
Diagram to show changing state. Which words go into the boxes?
EVAPORATE, CONDENSE, MELT and FREEZE
Place mouse over image to see the answers
