4. Irreversible Changes
What is an Irreversible change?
An Irreversible change is a permanent change that
cannot be undone.
For Example:
Baking a cake, Frying an egg, 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.
Heating
Cooling
Molten Wax
Candle Wax
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.
Heating
Cooling
Evaporating
Condensing
Water Water vapor/steam
8. 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.
Cooling
Heating
Melting
Condensing
Water
Ice
9. 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.
10. 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.
