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ICSE Class 7 Chemistry Question 12 of 14

Matter and Its Composition — Question 11

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Question 13

Give a reason why solids and liquids co-exist at their melting points.

Answer

At melting point, solid start changing into liquid state. Heat is absorbed and it is used in change of state without any rise in temperature till all the solid has changed into liquid state. Hence, the two states i.e., solid and liquid co-exist at melting point.

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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