Physical verus chemical changes (reversible and irreversible changes
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Transcript of Physical verus chemical changes (reversible and irreversible changes
Learning Intention Success CriteriaTo 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
Irreversible ChangesWhat 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
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.
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.
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.
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.
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.
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.
Review
Cooking an eggChemical
Shredding paperPhysical
A new substance is formedChemical
Microwave a bowl of soupPhysical
Water changes in the water cyclePhysical
Car crash makes a dent in the carPhysical
Acid rain wears away rockChemical
Mixing paint coloursPhysical
SunburnChemical
Fire Fly lights upChemical
Physical or Chemical
CRYSTAL GEODES
