1. Physical and Chemical Change
Chapter 7

2. Physical and Chemical Change

3. Physical and Chemical Change
Physical change - a change in shape or state that does not produce a new substance
Chemical change - a change that results in a new substance being formed
Physical and Chemical Change

4. Physical Change: Changing State
By applying heat, a substance will change from a solid to a liquid (melting) or from a liquid to a gas (evaporation).
If cooled, a substance will change from a gas to a liquid (condensation) or from a liquid to a solid (freezing or solidification).
A few substances change directly from a solid to a gas (sublimation) or a gas to a solid (deposition)
Physical Change: Changing State

5. Physical Change: Changing State

6. Examples: melting and freezing
Melting – When ice melts in your mouth or when butter is spread on hot toast the butter melts, but no new substances are formed.
Freezing – When liquid water is put in the freezer to form ice cubes or when drops of liquid candle wax cool and become solid again, no new substances are formed.
Examples: melting and freezing

7. Examples: evaporation and condensation
Evaporation – Puddles of water dry faster in hot weather, but no new substances are formed.
Condensation – When you breathe out on a cold day, ‘fog’ comes out of your mouth. This ‘fog’ is water vapour in your breath condensing to form a mist of tiny liquid water droplets.
Examples: evaporation and condensation

8. Dry ice (solid carbon dioxide) undergoes sublimation at temperatures above -78.5oC.
Dry ice is used in smoke machines in theatres and concerts.
Iodine, graphite and naphthalene (mothballs) also undergo sublimation.
Example: Sublimation

9. States of matter: changing state

10. Mixing Mixing two substances is a type of physical change.
For example, mixing different coloured balls does not form new colours.
Mixing

11. When a solid (solute) is dissolved in a liquid (solvent), they form a solution.
A solution is a mixture.
By removing the solvent by evaporation, then the solute particles form crystals.
For example, sugar dissolved in water can be separated and so no new substances are formed.
Dissolving

12. Dissolving Sugar

13. Chemical Change Signs of a chemical change include: colour change
gas produced (bubbles)
a solid (precipitate) forming in a clear solution
energy is produced or observed in the form of heat or light.
Chemical Change

14. When something changes colour, a chemical change has occurred.
Burning a match, paper or toast produces a black powder, which is carbon.
When iron is exposed to water and oxygen, it turns orange-brown because iron oxide (rust) is produced.
Green apples ripening to turn red.
Bleaching or dying clothes or hair.
(Note - Mixing paint is not a chemical change because no new substances are formed).
Colour Change

15. The production of gas indicates a chemical change.
This may be in the form of bubbles, a new smell or smoke.
Adding vinegar to bicarbonate of soda, bubbles of carbon dioxide are formed.
Rotten eggs produce the gas hydrogen sulfide.
(Note – Boiling and sublimation are not chemical changes).
Formation of gas

16. Precipitation formation of a solid
When two solutions are mixed a new solid is produced, which indicates a chemical change
Pipes and drains form a precipitate when scale or lime deposits inside.
Kidney stones precipitate in the kidneys and are very painful.

17. Energy is produced or observed
When energy is produced or observed, in the form of heat, light or sound, this is a sign of chemical change.
There are two types of reactions:
Exothermic – releases energy (hot)
Endothermic – absorbs energy (cold)

18. Exothermic Reactions Fireworks Sparklers Burning magnesium ribbon
Lighting a match
Respiration (the body converts food into energy)
Hot pack
Exothermic Reactions

19. Endothermic Reactions
Cold pack
Photosynthesis (plants absorb sunlight to produce glucose)
Eating sherbet
Endothermic Reactions

20. Exothermic and Endothermic reactions

21. Module 7.1
Review Questions
(page 293)
Q1,2,3,4,6,7,8,11,12