Tamil Nadu Class 8 Science: Matter Around Us

Quick Summary

Matter Around Us is part of Term 1 in Class 8 Science. This chapter studies the properties of the three states of matter, the particle model, and the processes by which matter changes state.

Key Definitions

• Matter: Anything that has mass and occupies space.
• Solid: Has definite shape and volume; particles closely packed with strong forces.
• Liquid: Has definite volume but no definite shape; particles less tightly packed.
• Gas: Has no definite shape or volume; particles far apart with weak forces.
• Melting: Solid to liquid on heating.
• Freezing: Liquid to solid on cooling.
• Evaporation: Liquid to gas; can occur at any temperature below boiling point.
• Condensation: Gas to liquid on cooling.
• Sublimation: Solid directly to gas without passing through liquid state (e.g., dry ice, camphor).
• Physical change: Change in physical properties; no new substance formed.
• Chemical change: Change that produces a new substance with new chemical properties.

Comparison of States of Matter

Changes of State

• Solid → Liquid: Melting (add heat)
• Liquid → Solid: Freezing (remove heat)
• Liquid → Gas: Evaporation / Boiling (add heat)
• Gas → Liquid: Condensation (remove heat)
• Solid → Gas: Sublimation (add heat)
• Gas → Solid: Deposition (remove heat)

Physical and Chemical Changes

Physical Changes

• No new substance formed.
• Reversible (usually).
• Examples: tearing paper, dissolving sugar in water, melting ice.

Chemical Changes

• New substance(s) formed.
• Usually irreversible.
• Examples: burning of wood, rusting of iron, curdling of milk.

Important Questions

One Mark

• What is sublimation? Give one example.
• Define matter.
• Name the process by which liquid changes to gas below its boiling point.
• Is rusting of iron a physical or chemical change?
• What happens to particle spacing when a solid melts?

Short Answer (3 marks)

• Distinguish between physical and chemical changes with two examples each.
• Explain the particle model of matter for solids, liquids, and gases.
• What is sublimation? Give two examples and one industrial use.

Long Answer (5 marks)

• Describe the three states of matter. Compare their properties in a table. Explain the changes of state using a labelled diagram.
• Differentiate between evaporation and boiling. Explain the factors that affect the rate of evaporation with examples from daily life.

Common Mistakes

• Saying evaporation only occurs at 100°C — it can occur at any temperature.
• Confusing condensation with evaporation.
• Treating all reversible changes as physical (some chemical changes can be reversed).

Revision Checklist

• [ ] Textbook reading completed
• [ ] Changes of state with correct terms written
• [ ] Physical vs chemical change examples noted
• [ ] Comparison table of three states of matter completed
• [ ] Important questions answered in notebook