1. PHYSICAL CHANGE vs CHEMICAL CHANGE

2. Physical change:
Physical change is one that is temporary and reversible.
No new substance is formed during a physical change.

3. Example 1 ICE - WATER - STEAM (They are all water!)
Ice melting to water or water boiling.
In all of these changes, you can get the original materials back!
Any change of state is ‘Physical Change’

5. melting Melting is a change from solid to liquid.
During melting heat is added.

6. evaporation Evaporation is a change from liquid to gas.
During evaporation heat is added.

7. condensation Condensation is a change from gas to liquid.
During condensation heat is removed.

8. freezing Freezing is a change from liquid to solid.
During freezing heat is removed.

9. sublimation Sublimation is a change from solid to gas.
During sublimation heat is added.

10. deposition Deposition is a change from gas to solid.
During deposition heat is removed.

11. Example 2
A physical change may also involve changing the shape of the substance.
Paper cut into pieces is still paper
Cutting wood into pieces is still wood
Molding a sculpture is still cement or marble!
Cutting is a ‘Physical Change

12. Example 3 Dissolving of salt in water is a physical change.
Salt can easily be recovered from salt water by evaporation.
Similarly mixing of two substances that do not react with each other is an example of physical change.
Mixing and dissolving is ‘Physical Change’

13. Chemical change
Chemical change is one where a new substance is produced.
The new substance is different from the original - has properties that are different than those of the starting materials.

14. Chemical change
This change is permanent and cannot be easily reversed using simple physical experiments.
Original materials cannot be obtained back easily.

15. Examples of chemical change
raw egg becomes cooked egg
cake mix becomes cake
paper becomes ash
steel becomes rust

16. Evidence of chemical change
Colour change
Odour
Temperature change
Production of light
Formation of a new solid inside a liquid
Production of a new gas – bubbles seen

17. Heat and chemical change
As seen earlier, heat is used to bring about some changes in state.
However, applying heat to a substance can also result in chemical changes

18. When baking powder is heated it undergoes a chemical change that results in the production of carbon dioxide gas (CO2)
This is very useful in cooking/baking
It is this chemical reaction that allows baked food to become light and fluffy
Cooking is an example of chemical change

19. Combustibility is the ability of a substance to react quickly with oxygen to produce heat and light
Burning is another example of a chemical change involving heat

20. When some substances are mixed, their reaction absorbs heat.
a chemical cold pack