Question 3
Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in the air, but to do the same through a solid block of wood, we need a karate expert.
(a) Gas is a state of matter in which intermolecular attraction is very weak and intermolecular space is so large that the particles become completely free to move randomly in the entire available space. Hence, it fills completely the vessel in which it is kept.
(b) Gas molecules have negligible intermolecular forces and possess high kinetic energy, enabling them to move rapidly in all directions. This random motion leads to collisions among particles and with the container walls, resulting in the exertion of pressure by gas particles on the container.
(c) A solid is characterized by a fixed shape and volume, and a wooden table also has these properties with its definite shape and volume, minimal intermolecular spaces, and rigidity. Therefore, it is appropriately called as a solid.
(d) Air particles have very weak intermolecular force of attraction and hence very large intermolecular spaces. As a result, we can move our hands freely in the air. The particles in a solid block, on the other hand, are bound together by a strong force of attraction. As a result, there is no space between them. Hence, we will require a karate expert.
Chapter 1: Matter in Our Surroundings — Quick Reference
Quick Revision Points
- Matter has mass and occupies space; made of particles with spaces, motion, and attraction
- Three states: Solid (fixed shape/volume), Liquid (fixed volume, not shape), Gas (neither fixed)
- Melting point of ice = 0°C (273 K); Boiling point of water = 100°C (373 K)
- Latent heat of fusion of ice = 334 J/g; Latent heat of vaporisation of water = 2260 J/g
- Sublimation: solid → gas directly (camphor, dry ice, naphthalene)
- Evaporation: surface phenomenon at all temperatures; causes cooling; factors: surface area, temperature, humidity, wind
- Temperature conversion: T(K) = T(°C) + 273
- Read the detailed chapter notes for complete coverage of all NCERT topics.
- Practice all NCERT in-text and back exercise questions — they are frequently asked in exams.
- Focus on comparison tables, diagrams, and definitions — these are high-scoring areas.
- For numericals (if applicable), practice at least 20 problems of varying difficulty.
- Refer to the practice question bank (200+ questions) for thorough preparation.
- Detailed Notes: ch01-matter-in-our-surroundings.html
- Practice Questions: 100+ questions with answers in 05-practice-questions/
- Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
- Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html