CBSE Class 9 > Class 9 Notes > Science > NCERT Textbook: Matter in Our Surroundings
NCERT Textbook: Matter in Our Surroundings
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FAQs on NCERT Textbook: Matter in Our Surroundings
| 1. What is the difference between solid, liquid, and gas in terms of particle arrangement? |  |
Ans. Solids have tightly packed particles in fixed positions with strong intermolecular forces, maintaining definite shape and volume. Liquids have loosely packed particles that move freely, taking container shape but keeping fixed volume. Gases have particles far apart with minimal intermolecular forces, spreading throughout available space with no fixed shape or volume. These three states of matter differ fundamentally in how their constituent particles are organised and interact.
| 2. Why do matter particles move faster at higher temperatures? | |
Ans. Increased temperature provides particles with greater kinetic energy, causing them to vibrate and move more rapidly. In solids, this faster vibration causes thermal expansion. In liquids and gases, particles move with increased speed and frequency, explaining why substances evaporate faster when heated. Temperature directly controls the motion of particles within any state of matter.
| 3. How does evaporation differ from boiling for Class 9 students? | |
Ans. Evaporation occurs at any temperature from the liquid surface when particles gain sufficient energy to escape as vapour. Boiling happens at a specific temperature throughout the entire liquid, with vigorous bubble formation. Evaporation is a slower process at lower temperatures, while boiling is rapid and occurs at the boiling point. Both involve phase change from liquid to gas but differ in speed, location, and temperature requirements.
| 4. What causes sublimation and which common substances undergo this process? | |
Ans. Sublimation occurs when solid particles gain enough energy to transform directly into gas without becoming liquid, bypassing the intermediate phase. Naphthalene (mothballs), dry ice, and iodine are common examples demonstrating sublimation in everyday life. This phase transition happens because particles at the solid's surface have sufficient kinetic energy to escape directly. Sublimation is temperature and pressure-dependent, occurring more readily at lower atmospheric pressures.
| 5. How do intermolecular forces affect the physical properties of matter? | |
Ans. Intermolecular forces determine how tightly particles bind together, directly influencing melting point, boiling point, and density. Strong intermolecular forces in solids like ice create rigid structures with high melting points. Weak intermolecular forces in gases allow particles to spread freely. Compressed gases and cooled substances increase intermolecular attractions, explaining why matter changes states and behaves differently across solid, liquid, and gaseous forms.
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NCERT Textbook: Matter in Our Surroundings of Science Class 9 is the updated edition as per the latest syllabus of the 2026-27, PDF available for download.
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