Changes around us through learning and observations

Chemistry around us observations inferences

1. Chemical and Physical Change Physical change: changes where ultimately no change in the chemical composition occurs – easily reversible Change of state (melting, boiling etc.) Dissolving Chemical change: a change where a chemical reaction occurs

2. Is it Chemical or physical change ? Grape juice turns to wine Wood burns to ashes Water boils Leaves turn yellow in Fall Rock is crushed to powder Salt dissolves in water 4

3. How to identify the change ?   Macroscopic Definition Microscopic Definition Physical Change The matter is the same. The original matter can be recovered. The particles of the substance are rearranged . Chemical Change The matter is different. The old matter is no longer present. The original matter cannot be recovered. The particles of the substance are broken apart, and the atoms are rearranged into new particles, forming a new substance. 6

4. Physical Changes Chemical Changes Aluminum foil is cut in half . Milk goes sour. Clay is molded into a new shape. Jewelry tarnishes. Butter melts on warm toast. Bread becomes toast.

5. A change can't be both physical and chemical , but physical and chemical changes can occur simultaneously. This is what's happening with the burning candle: the wax is melting, which is a physical change , and it's combusting, which is a chemical change . Video on physical change https://www.youtube.com/watch?v=cmrj2XO61FM Animation on physical and chemical changes https://www.youtube.com/watch?v=M8tyjwB42X4 Evidence of chemical reaction Video: https://www.youtube.com/watch?v=JSiBSSFKRwE 10

6. Physical change: changes where ultimately no change in the chemical composition occurs – easily reversible Chemical change: a change where a chemical reaction occurs- irreversible Water evaporates from the surface of the ocean. Rust forms on a nail left outside. A juice box in the freezer freezes. Gasoline is ignited. Rubbing alcohol evaporates on your hand. Hydrogen peroxide bubbles in a cut.  Dissolution of sugar Food scraps are turned into compost in a compost pile.  melting of ice A match is lit.  Boiling of water You take an antacid to settle your stomach.  tearing / folding paper Your body digests food.  mixing milk and water You fry an egg. 11

7. Match the column Column A Column B A change in which new substance is formed Non-periodic change Changes in which physical properties like shape, size and state changes without formation of new substance Slow change Those changes which take place in a long period of time Undesirable changes Those changes which we do not want to take place Chemical changes A change that does not repeat again and again after a regular interval of time Physical changes Burning of fuel is a Irreversible change

8. Use the definition to answer true or false State True or False (a) Evaporation of water is a reversible change. (b) Burning of the candle is an irreversible change. (c) Rusting of iron is a reversible change. (d) Bursting of cracker is fast change. (e) Formation of Petrol is a slow change. (f) Baking of dough into bread is a reversible change Irreversible change are those changes which are permanent changes and cannot be brought back into its original form A reversible change is a physical change that can be undone. A final substance can be converted back to the original substance without creating any new material. .