3. Learning Intention Success Criteria
To analyse the observation prac results
To become familiar with Chemical and Physical Changes.
To become familiar with reversible and irreversible changes.
To set up Crystal Geodes
4. Irreversible Changes
What is an Irreversible change?
An Irreversible change is a permanent change that
cannot be undone.
Baking a cake
Frying an egg
Metal
rusting
Mixing cement
Burning paper
5. Irreversible Changes
• Are Chemical reactions.
• Start with a material and end up with one or
more new ones.
• The new material is completely different from the
original one.
• Sometimes the new material is useful and
sometimes it is not.
• Sometimes microorganisms such as bacteria and
yeast are used to create irreversible changes.
6. Reversible Changes
What is a reversible change?
A reversible change is a change that can be undone or
reversed.
When chocolate is warmed it
melts and turns into a liquid. It
can be turned back into a solid
again by cooling .
Orange juice can be frozen to form a
solid icy pole. When it melts it becomes
liquid again.
When candle wax is heated it
becomes liquid and as it cools it
becomes a solid again.
7. Boiling, evaporating and condensing (changing a gas into a
liquid)
If you could capture all the steam that is made when a kettle
boils, you could turn it back to water by cooling it.
Dissolving:- When salt is mixed with water it disappears because
it dissolves in the water to make salty water. But the salt can be
recovered from the salty water by boiling off the water.
8. Reversible Changes/Physical Changes
• Are called Physical changes
• A reversible change can change the way a
substance looks or feel (its physical
appearance) and then it can change back to
its original appearance again.
• The change may affect its size, shape or form
BUT -
• A new substance is not formed.
9. Irreversible Changes/Chemical Changes
• Are called Chemical changes
• Cannot be undone – eg a cake you bake
cannot be turned back into eggs, flour, sugar
or oil.
• Changes occur at a molecular level where
bonds are broken
AND
• New products are formed.
10. Chemical Change Checklist Physical Change Checklist
-------- A new substance was created
-------- The change cannot be reversed
-------- Gas bubble may be present
-------- Heat, light or smoke may be
released
-------- There may be a smell
--------- No new substance is created
--------- The changed can be reversed
--------- There is a change in state ie
freezing, melting, condensing
or evaporating
--------- There is a change in
appearance, texture, size,
shape or form.
11. R
e
v
i
e
w
Cooking an egg
Chemical
Shredding paper
Physical
A new substance is formed
Chemical
Microwave a bowl of soup
Physical
Water changes in the water cycle
Physical
Car crash makes a dent in the car
Physical
Acid rain wears away rock
Chemical
Mixing paint colours
Physical
Sunburn
Chemical
Fire Fly lights up
Chemical
Physical or Chemical
