Question

H. Answer the following questions in brief.
1. Write two reversible changes.
2. Physical changes can be reversible as well as irreversible, Justify with appropriate exam
3. Respiration is a chemical change. Explain
4. Burning of a candle involves both physical and chemical changes. Explain the two type
5. Give two applications of expansion and contraction from day-to-day life.​

Answer 1

Answer:

Examples of reversible reactions include dissolving, evaporation, melting and freezing.

Answer 2

Answer:

1. Reversible changes

Examples of reversible reactions include dissolving, evaporation, melting and freezing.

2.Physical changes may or may not be reversible changes. Like, turning of water into ice is an example of reversible changes but growth in height is an irreversible change. ... All chemical changes are irreversible changes. Once the chemical properties of a substance are changed, it becomes another substance.

3.Respiration is a chemical change as new substances like carbon dioxide and water are formed. Also there is change in the mass as glucose is oxidised by oxygen and heat is released. This change is permanent. All these factors conclude that respiration is a chemical change.

4.A burning candle produces wax vapours which solidify and form wax again is physical change. At the same time wax on burning produces water vapours and carbon - dioxide which escape into the atmosphere which are new substances with new properties. ... Hence burning of candle shows both physical and chemical changes

5.1) Engines of motor vehicles run when gases expand. 2) When making steel rims for wheels. 3) When the screw-cap of a bottle cannot be opened.