Classify the changes involved in the following processes as physical or chemical changes:
- Photosynthesis
- Dissolving sugar in water
- Burning of coal
- Melting of wax
- Beating aluminium to make aluminium foil
- Digestion of food
Answer:
(a) It results in the production of new substances (such as food for plants and CO2 ).
- Hence, Photosynthesis is a chemical change.
(b) It is a temporary change, and sugar crystals can be obtained back from water through heating.
- Hence, dissolving sugar in water is a physical change
(c) Burning is always accompanied by the evolution of heat and ligh t and is irreversible .
- Hence, burning of coal is a chemical change
(d) Melting of wax leads to a change in the state of wax and is reversible .
- Hence, melting of wax is a physical change.
(e) Beating aluminium leads to a change in shape but leads to no changes in the properties of aluminium.
Therefore, beating aluminium to make aluminium foil is a physical change.
(f) Digestion of food involves chemical reactions , absorption and formation of new products in the digestive system.
Therefore, digestion of food is a chemical change.
