States of Matter GCSE

Question 1

Physical or Chemical Change

Answer 1

A physical change can be reversed such as water freezing into ice and ice melting back to water.
A chemical change cannot be reversed such as wood being burnt on a fire – you cannot get the wood back when it cools down. A new product is formed.

Question 2

Changes of State

Answer 2

Between particles there are intermolecular forces which are weak forces of attraction.
Energy is required for these forces to be broken.
When a solid is heated its temperature increases until it reaches it’s melting point.
At its melting point all of the energy is used to overcome some of the intermolecular forces that are holding the particles together. That means that the temperature stays the same at the melting point.
Once in it’s liquid form the temperature will then increase again until it reaches it’s boiling point.
At it’s boiling point all the energy is being used to overcome the intermolecular forces so that the particles can move in a random pattern and are not held together by any intermolecular forces.

Question 3

The State of a Substance

Answer 3

You can predict the state of a substance if you know it’s temperature and it’s melting point and boiling point.
Below the melting point a substance is solid.
Between the melting point and boiling point it is a liquid.
Above the boiling point it is a gas.
The melting point is where a substance starts to melt

Question 4

Melting, evaporating and boiling

Answer 4

Energy must be transferred, by heating, to a substance for these changes of state to happen. The energy is used to overcome:

some of the forces of attraction between particles during melting
all the remaining forces of attraction between particles during evaporating or boiling