Exercise Questions and Answers
Q1: Choose the correct option. The primary difference between solids and liquids is that the constituent particles are:
(i) closely packed in solids, while they are stationary in liquids.
(ii) far apart in solids and have fixed position in liquids.
(iii) always moving in solids and have fixed position in liquids.
(iv) closely packed in solids and move past each other in liquids.
A1: (iv) closely packed in solids and move past each other in liquids.
Explanation: Solids have closely packed particles with strong interparticle forces, restricting movement to vibrations. Liquids have weaker forces, allowing particles to move past each other, giving liquids no fixed shape.
Q2: Which of the following statements are true? Correct the false statements.
(i) Melting ice into water is an example of the transformation of a solid into a liquid.
(ii) Melting process involves a decrease in interparticle attractions during the transformation.
(iii) Solids have a fixed shape and a fixed volume.
(iv) The interparticle interactions in solids are very strong, and the interparticle spaces are very small.
(v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room.
(vi) On heating, we are adding energy to the camphor, and the energy is released as a smell.
A2:
(i) True: Melting ice into water is a transformation from solid to liquid.
(ii) False: The melting process involves particles gaining enough thermal energy to overcome interparticle attractions, not a decrease in the attractions themselves.
Corrected: The melting process involves particles gaining thermal energy to overcome interparticle attractions, allowing them to move apart.
(iii) True: Solids have a fixed shape and volume due to strong interparticle forces and close packing.
(iv) True: Solids have strong interparticle interactions and minimal interparticle spaces.
(v) True (T) ✅ — Camphor sublimates, and its vapour diffuses through the air, carrying the fragrance to all parts of the room.
(vi) False (F) ❌ — On heating, we add energy to the camphor, causing it to change into vapour; the smell is not energy release, but the vapour molecules reaching our nose.
Q3: Choose the correct answer with justification. If we could remove all the constituent particles from a chair, what would happen?
(i) Nothing will change.
(ii) The chair will weigh less due to lost particles.
(iii) Nothing of the chair will remain.
A3: Correct Answer: (iii) Nothing of the chair will remain.
Justification: A chair, like all objects, is made up of constituent particles such as atoms and molecules, which are held together by various forces (e.g., chemical bonds, intermolecular forces). These particles define the chair’s structure, mass, and physical properties. If we could remove all the constituent particles:
Option (i) Nothing will change: This is incorrect because removing all particles would eliminate the chair’s physical existence, as the chair is fundamentally composed of these particles. Without them, there would be no material or structure left.
Option (ii) The chair will weigh less due to lost particles: This is also incorrect. Weight is a measure of the force exerted by the mass of the chair due to gravity, and mass is determined by the total number of particles. If all particles are removed, the chair would cease to exist, and the concept of weight would no longer apply.
Option (iii) Nothing of the chair will remain: This is correct. Removing all constituent particles would mean disassembling the chair at its most fundamental level, leaving no material or physical form behind. The chair would effectively disappear, as its existence depends entirely on the presence of these particles.
Conclusion– The removal of all constituent particles results in the complete disappearance of the chair, making (iii) the correct answer.
Q4: Why do gases mix easily, while solids do not?
A4: Gases mix easily because the molecules in a gas are far apart and move very quickly in all directions. This high speed and large spacing mean they can spread out and intermingle without much restriction. In solids, the particles are tightly packed in fixed positions and can only vibrate in place, so they cannot move freely to mix with particles of another solid.
Q5: When spilled on the table, milk in a glass tumbler, flows and spreads out, but the glass tumbler stays in the same shape. Justify this statement.
A5: Milk flows and spreads out because it is a liquid, and in liquids, particles are close together but can slide past each other. This allows a liquid to take the shape of its container and flow when poured. The glass tumbler keeps its shape because it is a solid, and in solids, particles are tightly packed in fixed positions, so they can only vibrate but cannot move around. This rigidity makes a solid maintain its own shape.
Q6: Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.
A6:
Q7: Draw a picture representing particles present in the following: (i) Aluminium foil (ii) Glycerin (iii) Methane gas
A7:
Q8: Observe Fig. 7.16a, which shows the image of a candle that was just extinguished after burning for some time. Identify the different states of wax in the figure and match them with Fig. 7.16b showing the arrangement of particles.
A8: In Fig. 7.16a, the candle shows:
- Solid wax: The unburned wax, with closely packed particles vibrating in fixed positions (matches Fig. 7.16b, solid state).
- Liquid wax: The melted wax around the wick, with particles moving freely within a limited space (matches Fig. 7.16b, liquid state).
- Gaseous wax: The wax vapor that burns, with particles moving freely in all directions (matches Fig. 7.16b, gaseous state).
Q9: Why does the water in the ocean taste salty, even though the salt is not visible?
A9: Ocean water tastes salty because salt dissolves into its constituent particles, which are too small to be seen. These particles spread among water particles, occupying interparticle spaces, and can be detected by taste.
Q10: Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
A10: Grains of rice and rice flour are solids. They appear to take the shape of the container because their small particles can flow and settle, but each grain or particle retains its own fixed shape and volume, characteristic of solids, due to strong interparticle forces.