Chapter 7: Physical and Chemical Change

Question 1

Define physical change as being a change in which no new substance is formed.

Answer 1

The physical properties of a substance may change, but the substance before and after the change is exactly the same. Therefore, physical changes can often easily be reversed.

Question 2

Give examples of physical change in changes in shape

Answer 2

Breaking glass

Question 3

Give examples of physical change in expansion and contraction

Answer 3

When solids, liquids and gases are heated, expansion takes place. The volume of the object increases and its density decreases, but no new substances are formed
The opposite occurs when a solid, liquid or gas is cooled. It contracts as the volume of the substance decreases and its density increases.

Question 4

Give examples of physical change in change of states

Answer 4

butter is spread on hot toast

Question 5

Give examples of physical change in mixing

Answer 5

In this ball pit you can see the different coloured balls. It is an example of a mixture that can be seen with the naked eye. The different balls mix, but no new balls are formed.

Question 6

Describe melting in changes of state

Answer 6

Melting: (a solid to a liquid)
- You put an icecube in your mouth

Question 7

Describe freezing in changes of state

Answer 7

Freezing: (a liquid to a solid)
- Liquid water is put in the freezer to form ice cubes

Question 8

Describe evaporation in changes of state

Answer 8

Evaporation: (a liquid to a gas)
- Drying clothes on the line

Question 9

Describe condensation in changes of state

Answer 9

Condensation: (a gas to a liquid)
- When warm, moist air cools as it rises, water vapour condenses into tiny droplets, creating fog.

Question 9

Describe ways to detect the presence of a new substance

Answer 9

• seeing a colour change
• smelling gas or seeing bubbles
• seeing a new solid (known as a precipitate) forming in a clear solution
• seeing light or feeling a change in temperature

Question 10

Describe some examples of colour change that indicate chemical

Answer 10

A leave falling of a tree and changing it colour, dying your hair or mixing colours togethe

Question 11

Describe examples of gas formation that are chemical

Answer 11

Burning wood - if you burn wood you get a new smell and it is smoking/burning

Question 12

Describe the structure of solids, liquids and gases

Answer 12

Solid: are touching with very little space between them
Liquid: still touching but there are vibrating
Gas: big distances between them.