Physical N Chemical Changes 5ya4l

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 matter II. Matter around us undergoes changes. These changes can be classified into two types - physical changes - chemical changes

Physical changes • 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 • No new substance is form during a physical change. • 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 1. Examples a) Changes of physical state •

Caused by heating Ice

•

steam

Caused by cooling Steam

•

water

water

ice

No new substance form because H2O remain H2O

Physical changes a) Dissolving a solid in water dissolved aqueous sugar ( larutan Sugar + water gula)

•

Reverse changes Aqueous sugar

Aqueous sugar

evaporated

distillation water

sugar + water

sugar +

Physical changes a) 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

Chemical Changes • Changes of matter that produce new substance • The new substance have chemical properties which are different from the original substance • Chemical changes are usually difficult to reverse. This means that the product formed cannot be easily changed back into the reactant

Chemical Changes 1. Example a) Burning of paper Paper

Burn

ash + carbon dioxide

but Cannot be Ash + carbon dioxide

paper

Chemical Changes a) Browning of a peeled apple

Peeled apple

Exposed to air

browning apple

Chemical Changes a) Combustion of feul Hydrocarbon + oxygen carbon dioxide + oxygen

Chemical Changes a) Photosyntesis

Carbon dioxide + water (in plant)

light

glucose + oxygen

Examples in daily life Physical changes in Chemical changes daily life 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 Melting of chocolate

Decomposition of fallen leaves

Evaporate of sweat

Photosynthesis in green plants

Digestion of food in our body

Comparison between physical and chemical changes Chemical changes

Physical changes SIMILARITIES

Substance in both processes undergo changes Both changes require energy DIFFERENCES In term of No

Formation of new substance

Yes

reversible

Reversibility

Difficult to reverse

Less energy is needed

Amount of More energy is energy required needed

Changes in physical properties only

Change in properties

Changes in chemical and physical properties

Comparison between physical and chemical changes Chemical changes

Physical changes SIMILARITIES

Substance in both processes undergo changes Both changes require energy DIFFERENCES In term of No

Formation of new substance

Yes

reversible

Reversibility

Difficult to reverse

Less energy is needed

Amount of More energy is energy required needed

Changes in physical properties only

Change in properties

Changes in chemical and physical properties