Chemical change     Physical change   The three states of matter    Change in Mass

In a physical change no new substance is formed
Examples of physical change are: evaporation, melting, freezing and condensation.
Physical changes are usually temporary and can often be reversed

In a chemical change a chemical reaction is taking place and a new substance is always formed
Examples of chemical change are decomposition, oxidation and combustion.
Chemical changes are usually permanent and cannot easily be reversed.

eg: copper carbonate decomposes when heated to form carbon dioxide gas and leave black copper oxide.

Word equation: Copper carbonate ---------> copper oxide + carbon dioxide

2.    Oxidation
: When a chemical combines (joins up with) oxygen to form an oxide.

eg copper foil will oxidise when heated strongly in air

Word equation: copper + oxygen -------> copper oxide

3. Combustion (or burning) is a kind of oxidation where a flame is usually produced.

eg Magnesium will burn in air to form magnesium oxide:

Word equation: Magnesium + oxygen -------> magnesium oxide

Signs for a chemical change are:

1. A change in colour ( eg changes from pink to blue)

2. A change in temperature (eg gets warm or hot)

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Physical change

 All of the terms described below are types of physical change because no new substance is made and the changes are all reversible

getting hotter: 
MELTING : 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.

EVAPORATING: When a liquid turns to a vapour

BOILING: This is when a liquid turns to a vapour at its boiling point. 
eg WATER boils when heated.

SUBLIMING : 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
CONDENSING: This is when a vapour turns to a liquid when it is cooled down (to below the boiling point)

FREEZING (or solidifying): This is when a liquid turns to a solid. This happens when the liquid cools to below its melting point.

SUBLIMING : 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]

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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

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 = 100 C
Melting point = 0 C

We can make a substance change state by heating it up or cooling it down as described below.

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The Change in Mass when a chemical is heated

When certain elements are heated like magnesium or copper they will gain in mass.   (See table above)
They do this because they combine with oxygen.

To find out if there is a change in mass the chemical needs to be weighed before and after heating.

Example 1: Copper foil will gain in mass when heated in air because the copper oxidises (combines with oxygen)
Word equation: copper + oxygen -------> copper oxide

Example 2: Magnesium will gain in mass when it burns because the magnesium combines with oxygen however care must be taken to make sure that the smoke produced all gets weighed (See Burning Magnesium).

When compounds that decompose are heated they will often LOSE mass

Example 1:   When copper sulphate is heated it will lose mass because it decompose and give off water vapour.  (See experiment to heat copper sulphate)

Example 2:  When Copper carbonate is heated it will lose mass because it decomposes and gives off carbon dioxide gas.