Chapter 2 – Physical And Chemical Change

Selina Concise Chemistry 2023 solutions for class 8 Chemistry. Chapter 2 – Physical And Chemical Change is provided here with simple step-by-step explanations. These solutions for Physical And Chemical Change are extremely popular among class 10 students. The Physical And Chemical Change solution comes in handy for quickly completing your homework and preparing for exams.

Question 1

Define :

1. a physical change
2. a chemical change

Answer

1. A physical change is a change in which the substance undergoes a change in its physical state, such as a change in shape, size, or state of matter, without altering its chemical composition.
2. A chemical change is a change in which a substance undergoes a chemical reaction and forms one or more new substances with different chemical properties.

Question 2

Classify the following as a physical or a chemical change:

1. Drying of wet clothes
2. Manufacture of salt from seawater
3. Butter getting rancid
4. Boiling of water
5. Burning of paper
6. Melting of wax
7. Burning of coal
8. Formation of clouds
9. Making of a sugar solution
10. Glowing of an electric bulb
11. Curdling of milk

Answer

Question 3

Fill in the blanks :

1. The process of a liquid changing into a solid is called ____
2. A change which alters the composition of a substance is known as  ____ change.
3. There is no change in the ____ of the substance during a physical change.
4. The reaction in which energy is evolved is called ____

Answer

1. The process of a liquid changing into a solid is called solidification or freezing.
2. A change which alters the composition of a substance is known as chemical change.
3. There is no change in the chemical nature of the substance during a physical change.
4. The reaction in which energy is evolved is called exothermic reaction.

Question 4

Give a reason

1. Freezing of water to ice and evaporation of water are physical changes.
2. Burning of a candle is both a physical and a chemical change.
3. Burning of paper is a chemical change.
4. Cutting off a cloth piece is a physical change, though it cannot be reversed.

Answer

1. Freezing of water to ice and evaporation of water are physical changes because they do not involve any chemical reaction, and the chemical composition of water remains the same. In freezing, the water molecules slow down and come closer to each other to form a solid, while in evaporation, the water molecules gain energy and move apart to form a gas.
2. Burning of a candle is both a physical and a chemical change. The melting of wax is a physical change as it changes the state of matter, but the burning of the wick involves a chemical reaction that produces light, heat, and new substances such as carbon dioxide, water vapor, and ash.
3. Burning of paper is a chemical change because it involves a chemical reaction that changes the composition of paper and produces new substances such as ash, smoke, and gases.
4. Cutting off a cloth piece is a physical change because it only changes the shape of the cloth and does not alter its chemical composition. It cannot be reversed because the cut edges of the cloth cannot be perfectly joined to restore the original piece.

Question 5

Give four differences between physical and chemical changes.

Answer