1. Physical and Chemical Changes and Processes
CHAPTER 7
Physical and Chemical Changes and Processes

2. Introduction Changes in materials are going on around us all the time.
Leaves changes their colour
Trees shed their leaves
Milk changes to curd
Iron nails rusts in moisture
Some changes around us are slow and some are fast. In this chapter we will study about changes in matter.

3. What is a Physical Change?
A physical change alters the form of a substance, but does not change it to another substance.
Example:
Making Orange Juice

4. What is a Chemical Change?
When a substance undergoes a chemical change, it is changed into a different substance with different properties.
Example: Baking a Cake

5. Physical Change
Definition: A physical change is one in which only the physical properties of a substance change and its chemical properties remain the same.
Explanation: A change in which matter looks different but is still the same matter
A change that affects the size, shape or color of a substance but does not affect its composition

6. Physical changes are temporary and can easily be reversed

7. Examples of Physical Change
Cutting paper
Mashing potatoes
Painting a wall
Breaking glass
Melting marshmallows
Molding clay
Water freezing
Water boiling
Thawing meat

8. Chemical Change
Definition: A chemical change is one in which a new substance is formed.
Explanation: A change that results in the formation of a new substance
A change that is permanent in nature
A change in materials that produces a new substance; the change is permanent

9. Chemical changes are permanent and not easy to reverse.

10. Examples of Chemical Changes
Wood burning to ash and smoke (a new substance is formed)
Iron rusting
Marshmallows burning
Apple rotting
Toasting bread

11. Raw Egg Becomes Cooked Egg

12. Cake Mix Becomes Cake

13. Signs of a Chemical Change
1. Color Change 2. Precipitation

14. 3. Gas Production
4. Temperature Change
Changes in Characteristic Properties (odor, light given off)

15. 5. Changes in Characteristic Properties (odor, light given off)

16. Chemical or Physical Change?
Cutting paper?
Physical

17. Chemical or Physical Change?
Ice melting?
Physical

18. Chemical or Physical Change?
Toast burning?
Chemical

19. Chemical or Physical Change?
Rocket fuel burning?
Chemical

20. Chemical or Physical Change?
Sawing wood?
Physical

21. Chemical or Physical Change?
Metal rusting?
Chemical

22. Chemical or Physical Change?
Disappearing puddle?
Physical

23. Phase Changes are PHYSICAL PHYSICAL!!!!!
Types of Phase Changes:
1. Melting
2. Freezing
3. Evaporization
4. Condensation
5. Sublimation
6. Deposition

24. Physical and Chemical Changes
Quiz
Number your paper (1-10)

25. 1. A. Physical Change B. Chemical Change
Rusting nails

26. 2. A. Physical Change B. Chemical Change
Effervescent tablet

27. 3. A. Physical Change B. Chemical Change
Cut paper

28. 4. A. Physical Change B. Chemical Change
Vinegar and Baking soda

29. 5. A. Physical Change B. Chemical Change
Salt and water

30. 6. A. Physical Change B. Chemical Change
Broken glass

31. 7. A. Physical Change B. Chemical Change
Burning wood

32. 8. A. Physical Change B. Chemical Change
Ice melting

33. 9. A. Physical Change B. Chemical Change
Removing iron filings from a mixture

34. 10. A. Physical Change
B. Chemical Change
Boiling water

35. Check your answers 1. B - Chemical 2. B - Chemical 3. A - Physical

36. Applications of Chemical Changes
As a result of chemical changes new substances are formed. We are living in the world of chemical changes. Chemical changes are taking place in our bodies. In our vehicles and in our environment.
Sometimes chemical changes form harmful substances.

38. Reversible and Irreversible changes
Reversible change: a change that can go forwards
or backwards, for example melting
and freezing .
Irreversible: a change that cannot go back, for
example burning

39. Irreversible changes Describe what happens in this example.
Do you think these can be reversed?
These are difficult to reverse as new products have been made.

40. Heating Materials Heating some materials causes them to change
Do you think they can be easily reversed?

41. Burning Materials
Do you think that the ash is the only material produced by burning the paper?
Gas is also produced.
What is the difference between heating an object and burning an object?
Do you think that when an object is burned the process can be reversed?
Can you think of other everyday examples of objects burning?

42. Burning A material is burned the change is irreversible
New materials are produced when materials are burned.
These are often hazardous.
Produce a poster warning people of the dangers of the fumes given off by burning materials in the home.

44. USE OF HYDROCARBONS AS FUELS
Burning of fuels is another example of a chemical change.
Fuel that we use to run our vehicles or factories consists of substances known as hydrocarbons.
A hydrocarbon is a compound consisting of only hydrogen and carbon atoms.

45. Combustion
Combustion Definition: Combustion is a chemical reaction chemical that occurs between a fuel and an oxygen that produces oxides of carbon, water vapours and energy, usually in the form of heat and light.

47. A fuel is a substance that burns to release energy
Each of these sides represents a key element for fire to occur. If one of them was removed, the triangle would collapse and the fire would go out

48. Incomplete Combustion
If there is insufficient air for complete combustion, incomplete combustion takes place.
Hydrogen is still oxidised to water, but carbon monoxide forms instead of carbon dioxide.
Carbon monoxide is a toxic gas, so adequate ventilation is important when burning fuels.

49. In limited oxygen Supply

50. Hydrocarbons are mostly obtained from crude oil (petroleum)
Hydrocarbons are mostly obtained from crude oil (petroleum). When hydrocarbons burn in the presence of oxygen their chemical composition change.
As a result of burning of hydrocarbons, a lot of heat is produced.
People use heat for various purposes such as cooking, heating, movement, etc.

51. Use of heat (cooking, heating, movement)