Change of State: Freezing MCQs Quiz | Class 9
Welcome to the Class IX Science (Code 086) quiz covering Unit I: Matter – Its Nature and Behaviour. This session focuses on the topic “Change of State: Freezing,” specifically addressing the process of freezing, the concept of heat release, and practical examples. Complete the 10 multiple-choice questions below to test your knowledge, then submit to check your score and download the comprehensive PDF answer key.
Understanding Freezing (Solidification)
Freezing is the process in which a substance changes its state from liquid to solid. This phase change occurs at a specific temperature known as the freezing point. During this process, the substance loses heat energy to the surroundings.
Key Concepts of Freezing
- Heat Release (Exothermic Process): Unlike melting, which requires heat absorption, freezing involves the release of latent heat. Even though heat is released, the temperature of the substance remains constant during the phase change until the entire liquid has solidified.
- Particle Behaviour: As a liquid cools, its particles lose kinetic energy and move more slowly. Eventually, the attractive forces between particles become strong enough to lock them into fixed positions, forming a solid structure.
- Freezing Point: The temperature at which the liquid and solid states of a substance exist in equilibrium. For pure water at standard atmospheric pressure, this is 0 degrees Celsius.
Comparison: Freezing vs. Melting
| Feature | Freezing | Melting |
|---|---|---|
| State Change | Liquid to Solid | Solid to Liquid |
| Energy | Released (Exothermic) | Absorbed (Endothermic) |
| Particle Motion | Decreases (Slows down) | Increases (Speeds up) |
| Forces of Attraction | Increases | Decreases |
Quick Revision Notes
- Freezing is also called solidification.
- The freezing point of a substance is the same as its melting point.
- Adding impurities (like salt to water) lowers the freezing point; this is why salt is used to melt ice on roads.
- During freezing, potential energy of particles decreases, but average kinetic energy remains constant while the temperature is stable.
Extra Practice Questions
- What happens to the density of water when it freezes? (Ideally decreases, forming ice which floats).
- Name the energy released during freezing without a change in temperature. (Latent heat of fusion).
- Does the temperature of water drop below 0 degrees Celsius while it is freezing? (No, it stays at 0 degrees Celsius until completely frozen).
- Why do farmers flood fields before a frost? (Water releases heat as it freezes, protecting crops).
- What is the state of matter where particles vibrate in fixed positions? (Solid).
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