CHAPTER 5: ENERGY AND CHEMICAL CHANGES

5.1 Physical and chemical changes

Introduction Living thing Non-living thing

I. Both living and non-living thing are matterII. Matter around us undergoes changes. These

changes can be classified into two types - physical changes - chemical changes

Physical changes

1. Physical changes in a substance is one that effect its physical properties, such as

• Shape

• Volume

• Density

• State of matter (solid,liquid,gas)

• Colour

• Mass

Physical changes

2. No new substance is form during a physical change.

3. Physical changes are usually reversible. This mean that the physical properties of the substance which has undergone a physical change can be changed back.

Water ice water

Physical changes 4. Examples

a) Changes of physical state

• Caused by heating

Steam water ice

Ice water steam

• Caused by cooling

• No new substance form because H2O remain H2O

Physical changes b) Dissolving a solid in water

Sugar + water aqueous sugar ( larutan gula)

• Reverse changes

Aqueous sugar sugar + water evaporated

dissolved

Aqueous sugar sugar + water distillation

Physical changes c) Crystallizing a salt from it saturated solution

• Saturated salt means a solution with

maximum quantity of the salt dissolved on

it.

• Solid salt can be obtained by crystalization

1. Changes of matter that produce new substance2. The new substance have chemical properties

which are different from the original substance 3. Chemical changes are usually difficult to

reverse. This means that the product formed cannot be easily changed back into the reactant

Chemical Changes

Chemical Changes

a) Burning of paper

4. Example

Paper ash + carbon dioxide Burn

but

Ash + carbon dioxide Cannot be

paper

Chemical Changesb) Browning of a peeled apple

Peeled apple browning appleExposed to air

Chemical Changesc) Combustion of feul

Hydrocarbon + oxygen carbon dioxide + oxygen

Chemical Changesd) Photosyntesis

Carbon dioxide + water glucose + oxygenlight

(in plant)

Examples in daily life Physical changes in daily life

Chemical changes in daily life

Freezing of water to form ice cube

Boiling an egg to get a hard-boiled egg

Boiling of water Burning of fossil fuel in motor vehicles

Dissolving sugar or salt in water

Respiration in living organism

Melting of wax to form different shapes of candles

Decomposition of fallen leaves

Melting of chocolate Digestion of food in our body

Evaporate of sweat Photosynthesis in green plants

No Formation of new substance

Yes

reversible Reversibility Difficult to reverse

Less energy is needed

Amount of energy required

More energy is needed

Changes in physical properties only

Change in properties

Changes in chemical and physical properties

Comparison between physical and chemical changes

Physical changes Chemical changes

SIMILARITIES

Substance in both processes undergo changes

Both changes require energy

DIFFERENCESIn term of

No Formation of new substance

Yes

reversible Reversibility Difficult to reverse

Less energy is needed

Amount of energy required

More energy is needed

Changes in physical properties only

Change in properties

Changes in chemical and physical properties

Comparison between physical and chemical changes

Physical changes Chemical changes

SIMILARITIES

Substance in both processes undergo changes

Both changes require energy

DIFFERENCESIn term of