Sub-Strand: 2.1 INVESTIGATING MATTER

Lesson Notes: Changes in States of Matter

1. States of Matter

• Matter exists in three main states: Solid, Liquid, and Gas.

2. Processes Involved in Changing States

• Melting – Solid to Liquid (e.g., ice melting into water).
• Freezing – Liquid to Solid (e.g., water freezing into ice).
• Evaporation – Liquid to Gas (e.g., water turning into steam).
• Condensation – Gas to Liquid (e.g., steam turning into water droplets).
• Sublimation – Solid to Gas (e.g., dry ice turning into gas).
• Solidification – Gas to Solid (e.g., frost forming on a cold surface).

3. Key Concepts

• Heat gain causes melting, evaporation, and sublimation.
• Heat loss causes freezing, condensation, and solidification.

4. Experiment & Observations

• Investigate the changes by heating and cooling different substances.
• Observe and record how heat affects the state of matter.

5. Safety Precautions

• Handle hot substances carefully.
• Use protective gear when needed.
• Follow teacher instructions.

6. Summary

• Matter can change states when heated or cooled.
• These changes are reversible in most cases.
• Observing these changes helps us understand real-world applications (e.g., water cycle, refrigeration).

Reversible and Irreversible Changes in Matter

1. Reversible Changes

A reversible change is one that can be undone, meaning the substance can return to its original state. These changes usually involve physical processes like melting, freezing, or dissolving.

Examples:

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• Melting Ice: When ice melts, it turns into water. If we freeze it again, it becomes ice again.
• Boiling Water: Water turns into steam when heated. If cooled, the steam condenses back into water.
• Dissolving Sugar in Water: Sugar dissolves in water, but if we evaporate the water, sugar crystals form again.

2. Irreversible Changes

An irreversible change is one that cannot be undone, meaning the substance forms something new. These changes usually involve chemical reactions like burning, rusting, or cooking.

Examples:

• Burning Paper: When paper burns, it turns into ash and smoke, which cannot be changed back into paper.
• Cooking an Egg: Heating changes the egg’s proteins permanently, so it can’t turn back into a raw egg.
• Rusting Iron: When iron reacts with water and oxygen, it forms rust. This change cannot be reversed easily.

Key Difference:

• Reversible changes only change the form of a substance, not its composition.
• Irreversible changes create a new substance with different properties.

Multiple Choice Questions (MCQs)

1. Which process changes a solid directly into a gas?
   A. Condensation
   B. Freezing
   C. Sublimation
   D. Melting
   Answer: C. Sublimation
2. What happens when water is heated and turns into steam?
   A. Freezing
   B. Condensation
   C. Evaporation
   D. Melting
   Answer: C. Evaporation
3. Which of the following is an irreversible change?
   A. Melting butter
   B. Freezing water
   C. Cooking an egg
   D. Dissolving salt
   Answer: C. Cooking an egg
4. What causes condensation to occur?
   A. Heat gain
   B. Heat loss
   C. Pressure increase
   D. Evaporation
   Answer: B. Heat loss
5. Which is a key difference between reversible and irreversible changes?
   A. Reversible changes form new substances
   B. Irreversible changes can be easily undone
   C. Reversible changes only change form, not composition
   D. Irreversible changes involve physical changes
   Answer: C. Reversible changes only change form, not composition

True or False

6. Freezing is a change from liquid to solid.
   Answer: True
7. Rusting is an example of a reversible change.
   Answer: False
8. Condensation is caused by heat gain.
   Answer: False
9. Sublimation skips the liquid state.
   Answer: True
10. Boiling water is an example of an irreversible change.
    Answer: False

Short Answer Questions

11. Name three states of matter.
    Sample Answer: Solid, Liquid, Gas
12. What type of change is melting ice – reversible or irreversible? Explain.
    Sample Answer: Reversible, because the water can be frozen back into ice.
13. Give an example of a change caused by heat loss.
    Sample Answer: Freezing water into ice.
14. Why is cooking an egg considered irreversible?
    Sample Answer: Because heat changes the egg’s proteins permanently, and it cannot return to its raw state.
15. List two safety precautions when experimenting with changes in matter.
    Sample Answer: Wear protective gear and handle hot substances carefully.

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