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


Changing state

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


 

Back to top of page