1. 20/09/2012
Chemical and Physical Reactions
Lesson Objectives:
•To know the difference between chemical and
physical reactions
•To detect the characteristic signs of a chemical
reaction
Key words: (Can you think of a good definition?)
•Reversible
•Irreversible

2. 20/09/2012
Question:
How can we tell if a chemical
reaction has happened?
Hands up if you have an idea

3. Chemical or Physical Change?
20/09/2012
• Lighting a match
Chemical
• Melting chocolate Physical
• Freezing water to make ice
Physical
• Frying an egg
Chemical
• Mixing paint to make a new colour Chemical

4. Chemical Changes
• Chemical changes result in the formation of a
new substance and tend to be irreversible.
• The following observations often suggest that
a chemical change has taken place:
• Colour change
• Evolution (release) of gas
• Temperature change
• Solution turns cloudy
• Change of pH

5. Physical Changes
• Physical changes do not result in the
formation of a new substance and are
reversible.
• The following are examples of physical
changes:
• Melting and freezing
• Boiling and condensation
• Forming a separable mixture

6. 20/09/2012
Finished?
Add 5 examples to your table from the list
below:
• Making toast
• Boiling an egg
• A light bulb getting hot
• Boiling water
• Adding sugar to a cup of tea
• Food going mouldy
• Setting off a firework
• Treating wasp and bee stings
• Diluting orange juice with water

7. Chemical or Physical?
candle burning rusty car puddles drying
egg frying fireworks frost forming