Physical and Chemical Changes:
https://www.youtube.com/watch?v=x49BtB5dOwg
1
Year 8 Science Chemistry
Connections
Week 5 Lesson 1
2
Chemical Properties, Chemical Reactions
Learning Intentions:
In this lesson, we will look at
• Physical and chemical change
Success Criteria:
By the end of the lesson, you will :
• Understand the differences between Physical and chemical
changes
• Recognise indicators for chemical change.
3
Chemical reactions are
happening everywhere.
Chemical reactions in your
body digest food, decay your
teeth and much more.
Chemical reactions occur in
batteries to provide electricity,
in the oven when you bake a
cake, in your hair when it is
bleached or coloured, and in
your car when it burns fuel.
Explosions are very fast
chemical reactions.
4
Check for Understanding
The change that happens in a battery is an example of a
1. Chemical Change
2. Physical Change
5
Check for Understanding
A fire is an example of a
1. Chemical Change
2. Physical Change
6
IN A CHEMICAL CHANGE NEW COMPOUNDS ARE FORMED
A chemical property is a characteristic of a
substance that is observed when it
undergoes a chemical change.
What Chemical change occurs when you
toast a marshmallow?
In a chemical change, the substances are
altered chemically and display different
physical and chemical properties after the
change. When a chemical change occurs new
substance(s) are formed through a
reorganization of the atoms. A chemical
change is difficult to reverse.
Examples:
• Magnesium wire burns producing a white ash of MgO.
• https://www.youtube.com/watch_popup?v=Ncx5yoCqw6A (3:31)
• When zinc is combined with hydrochloric acid, hydrogen gas is formed and a salt of zinc
chloride.
• When food is metabolized in the body, carbon dioxide and water is produced and energy
is released as heat.
7
In a combustion reaction new products
are formed.
1. True
Or
2. False
8
PHYSICAL PROPERTIES AND PHYSICAL CHANGE
Physical properties are properties of an element or
compound that can be observed without a
chemical reaction of the substance. Density and
electrical conductivity are examples of physical
properties.
In a physical change, the substances are not altered
chemically. No new products are formed.
Chemical bonds are not broken in a physical change
A physical change can affect the size, shape or colour
of a substance but does not affect its composition. The
substances may be changed to another phase (i.e. gas,
liquid, solid) or separated or combined.
Examples:
• When ice melts
• Sulphur is mixed with iron filings,
• Breaking a glass
• Dissolving sugar in water.
9
Watch the Video – ‘Chemical and Physical Changes’
https://www.youtube.com/embed/M8tyjwB42X4
When chemical reactions take place, such as rusting, the atoms of the element Iron combine
with water molecules and oxygen, to form a new compound, Iron Oxide (rust).
NEW COMPOUNDS FORM IN CHEMICAL REACTIONS
10
In this reaction, the reactants are the iron, water and oxygen and the product is the rust.
KEY INDICATORS - CHEMICAL REACTION
Use your key indicators to detect if a chemical reaction has taken place when something
rusts.
Which of the following indicators could you use as evidence to detect a chemical reaction?
Science Quest Chp. 8.4
Watch the following videos on Chemical Changes in this chapter.
11
Science Quest p.256
12
Learning Intentions:
In this lesson, we will look at
• Physical and chemical change
How did you go?
Success Criteria:
By the end of the lesson, you will :
• Understand the differences between Physical and chemical
changes
• Recognise indicators for chemical change.
13