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Chemical Changes

Chemical Changes. 1. What are the changes that can take place?. Physical changes Chemical changes. Make a guess which type of changes are these?. Cutting a piece of paper into several pieces. Physical changes / Chemical changes. Burning a piece of paper completely.

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Chemical Changes

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  1. Chemical Changes 1

  2. What are the changes that can take place? • Physical changes • Chemical changes

  3. Make a guess which type of changes are these?

  4. Cutting a piece of paper into several pieces Physical changes / Chemical changes

  5. Burning a piece of paper completely

  6. Iron rusting in the presence of water and oxygen Physical changes / Chemical changes

  7. Sweat on your skin slowly evaporates under sunlight Physical changes / Chemical changes

  8. MRT tracks expanding and contracting under different weather Physical changes / Chemical changes

  9. Lighting a bulb Physical changes / Chemical changes

  10. Photosynthesis of plants Physical changes / Chemical changes

  11. Definition of chemical Reaction • Chemical changes are permanent and irreversible • Produced new substances • Reactants are changed into products Example: reactant A + reactant B  product C + product B

  12. Definition of physical reaction • When a change is reversible, we call it a physical change • No new substance is formed

  13. Differences between physical and chemical changes

  14. What causes physical and chemical changes?

  15. Physical & chemical changes are brought about by interactions between matter and different forms of energy: • Heat • Light • Electricity or by • Combination of 2 different matter

  16. Chemical Changes Caused by Heat • Changes in State of Matter • Combination • Thermal Decomposition • Combustion

  17. Heat Causes Changes in the State of Matter • From Solid to liquid to gas or vice versa • Melting, freezing, boiling, evaporation • Sublimation: From solid change straight to gas These are physical changes since changes are reversible and no new products are formed

  18. Changes in states of matter

  19. Heat Causes Changes in the State of Matter • Some substances undergo sublimation • Like dry ice (carbon dioxide) and iodine • hyperlink (http://www.dac.neu.edu/physics/b.maheswaran/phy1121/data/ch04/anim/anim0406.htm)

  20. Expansion & Contraction • Expansion and contraction are also physical changes Why are electrical wires not hung tautly?

  21. Combination • Combination refers to a process in which two or more substances form a new substance Example Iron + Sulphur Iron Sulphide Fe + S FeS heat

  22. Combination 2K + Cl2 2K2Cl

  23. Combination 2Al + 3Br2 Al2Br6

  24. Combustion • Refers to combination of a substance with oxygen in the presence of heat. • One or more new substances may be produced

  25. Combustion • Can combustion take place on the moon? • No, unless there is a supply of air or oxygen present

  26. Combustion = Burning

  27. Combustion is a type of oxidation reaction • Processes such as rusting and combustion are oxidation reactions. • Oxidation refers to a process in which a substance reacts with oxygen

  28. Oxidation • Examples - Burning of magnesium in oxygen - Rusting of iron - Fireworks - Burning of paper or wood Rust Burning Mg

  29. Thermal Decomposition • A substance breaks down into 2 or more substances by effect of heat Example: sugar carbon + water vapour calcium carbonate calcium oxide + carbon dioxide heat heat

  30. Decomposition

  31. Chemical Changes Caused by Light • Photosynthesis • Photography • Obtaining energy from solar cells

  32. Chemical Changes Caused by Light • Photosynthesis: Process in which green plants make food in the presence of light sunlight carbon dioxide + water glucose + oxygen chlorophyll

  33. Chemical Changes Caused by Light

  34. Chemical Changes Caused By Light Under the exposure of light, chemical reaction takes place with the formation of new products Fading of the colour of newspaper due to light exposure

  35. Chemical Changes Caused By Light Example photographic films : coating of silver bromide silver bromide silver + bromine light

  36. Chemical Changes Caused By Light • Does chemical changes take place if a digital camera is used? • No, light is changed to electrical signals to form images in a digital camera.

  37. Chemical Changes Caused By Light • Why are silver nitrate solutions stored away from direct sunlight? • Exposure to direct sunlight will cause it to decompose.

  38. Chemical Changes Caused by Light • Solar cells are also called photovoltaic cells • They convert light energy directly into electricity

  39. Solar Cells Solar cells are used in areas where electricity is not readily available. Suggests some uses of this energy within the house. Solar Panels on House Roof

  40. Electricity The changes that takes place include: • Heating • Light production • Magnetic effect • Chemical effect • Electrolysis

  41. Heating a light bulb with electricity to produce light • A physical process • The filament in the light bulb is heated up, and electrical energy is converted to heat and light energy. No new substances are formed

  42. Splitting water using electricity • This process is called Electrolysis

  43. Chemical Changes Caused By Mixing Sodium hypochlorite + water  chlorine gas (bleaching) Also used in swimming pools:

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