1. Physical and chemical reactions
Compare physical & chemical changes and recognise signs of a chemical reaction

2. How do you know if a reaction is a physical one?
Is it reversible? Yes: then it is a physical reaction
Does a new substance appear? If no, then it is a physical reaction
Does a substance disappear? If it has just melted then it is a physical reaction
Has there been an energy change? Has it got hotter or colder? If no then it is a physical reaction

3. Simple examples of physical changes:
Ice melting: this is a change in state and is a common physical change.
All changes in state are physical reactions.
Sugar dissolving: this is a physical reaction as it can be reversed. The water just needs to be evaporated off.
When a substance is dissolved, it can be undissolved by removing the water through evaporation
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Bending a nail: this can be easily reversed by unbending it
A change in shape is just a physical reaction.

4. How do you know a reaction is a chemical reaction?
Is the reaction reversible? If no then it is a chemical reaction
Does a new substance appear? If yes, then it is a chemical reaction
Does a substance disappear? Has it dissolved? Then it is a chemical reaction, if it has just melted then it is a physical reaction
Has there been an energy change? Has it got hotter or colder? If yes then it is a chemical reaction

5. Examples of chemical reactions
Baking a cake: this can’t be reversed, you can’t unbake a cake.
Baking soda reacting with vinegar: a gas is given off, this is a new substance
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When the baking soda reacts with the vinegar it disappears: it is reacting.
When some chemicals are mixed there is a change in temperature: think about an instant ice pack: the chemicals are mixed and it gets very cold.

6. Basic experiments:
Aim: to observe a candle burning and decide where chemical and physical reactions are occuring
Method:
Light a candle
Write down your observations
Label a candle diagram showing what chemical and physical reactions are occuring

7. physical chemical physical chemical Results:
Observations: …
Conclusion: both chemical and physical reactions occur when a candle burns
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