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ICSE Class 7 Chemistry Question 9 of 14

Matter and Its Composition — Question 6

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Question 8

Give a reason why-

(a) Solids have a definite volume and a definite shape

(b) Liquids have a definite volume but no definite shape

(c) Gases have no definite volume and no definite shape.

Answer

(a) Solids have negligible intermolecular space as the molecules are closely packed and the force of attraction is maximum. This arrangement of molecules gives them a definite volume and a definite shape.

(b) In liquids the molecules are less tightly packed as compared to solids, so the intermolecular space is larger and force of attraction is weaker. This gives them a definite volume but no definite shape.

(c) In gases the molecules are far apart so the intermolecular space is very large and the force of attraction is the least. Hence, gases have no definite volume and no definite shape.

ICSE Class VII Chemistry Chapter 1 15 Marks

Matter and Its Composition — Quick Study Guide

Everything around us is made of matter. Matter has mass and occupies space. It exists in three states: solid, liquid, and gas. Each state has unique properties based on how particles are arranged and move.

Key Definitions

  • Matter: Anything that has mass and occupies space
  • Solid: Fixed shape and volume, particles closely packed
  • Liquid: Fixed volume but no fixed shape, particles slide over each other
  • Gas: No fixed shape or volume, particles move freely
  • Diffusion: Spreading of particles from high concentration to low concentration
  • Sublimation: Direct change from solid to gas (e.g., camphor)
  • Latent heat: Heat absorbed during change of state without temperature change

Important Comparisons

Evaporation vs Boiling: Evaporation is a surface phenomenon at all temperatures (slow, no bubbles). Boiling occurs throughout the liquid at a specific temperature (rapid, with bubbles).

Exam Tips

  • Learn all six interconversion processes with examples
  • Practice questions on predicting state at a given temperature
  • Know factors affecting evaporation (4 factors)
  • Understand why pressure cooker cooks faster

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