Year 9 Physics: Changes of State

What Are Changes of State?

Changes of state refer to how substances can change from one form to another. This happens when energy is added or removed, usually in the form of heat. The main states of matter are:

1. Solid: Has a fixed shape and volume. The particles are closely packed together and can only vibrate.
2. Liquid: Has a fixed volume but takes the shape of its container. The particles are close together but can move past one another.
3. Gas: Has no fixed shape or volume. The particles are far apart and move freely.

Key Changes of State

There are several important changes of state that you should know:

1. Melting: Solid to liquid. Example: Ice melting into water.
2. Freezing: Liquid to solid. Example: Water freezing into ice.
3. Evaporation: Liquid to gas. Example: Water evaporating into steam.
4. Condensation: Gas to liquid. Example: Steam condensing into water droplets.
5. Sublimation: Solid to gas. Example: Dry ice turning directly into carbon dioxide gas.
6. Deposition: Gas to solid. Example: Frost forming from water vapour in the air.

Key Rules to Remember

• Energy Change: When a substance changes state, energy is either added or removed.
  • Adding energy (heating) typically causes melting, evaporation, or sublimation.
  • Removing energy (cooling) typically causes freezing, condensation, or deposition.
• Temperature: During a change of state, the temperature remains constant until the change is complete. For example, when ice melts, the temperature stays at 0°C until all the ice has turned into water.

Tips and Tricks

• Use Visuals: Draw diagrams of the particle arrangement in solids, liquids, and gases to see how they change during state changes.
• Relate to Everyday Life: Think about how you see these changes every day, like making ice cubes or boiling water.
• Remember the Order: Keep the changes of state in mind using mnemonics or simple phrases (e.g., “Melting Makes Evaporation Cool Down”).

Questions on Changes of State

Easy Level Questions

1. What state of matter is ice?
2. What happens when water is heated?
3. What do we call the change from liquid to gas?
4. What is the process of water freezing called?
5. What state of matter has a fixed shape?
6. Name one example of sublimation.
7. What happens to particles in a solid when it melts?
8. What is condensation?
9. What do we call a gas turning into a solid?
10. Give an example of a liquid.
11. What happens to the temperature during melting?
12. What is the main difference between a liquid and a gas?
13. When ice melts, does it absorb or release energy?
14. What is the state of water at 100°C?
15. What is the opposite of evaporation?
16. What happens to a puddle of water on a sunny day?
17. Name a gas that can condense into a liquid.
18. What is the freezing point of water?
19. What happens to particles in a gas when it cools?
20. How does dry ice change state?

Medium Level Questions

1. Describe what happens to the energy during evaporation.
2. Explain why the temperature remains constant during boiling.
3. What is deposition, and where can you see it in nature?
4. How does the arrangement of particles change when a solid melts?
5. What happens to the volume of water when it freezes?
6. Why can a gas fill any container it’s in?
7. Describe an everyday example of condensation.
8. What state of matter do particles move the fastest?
9. How do pressure changes affect boiling point?
10. Explain how a thermometer works in relation to changes of state.
11. Why do we say that melting is a physical change?
12. What happens to the particles in a liquid when it freezes?
13. Describe the process of sublimation in detail.
14. How does the process of evaporation cool a liquid?
15. Why does snow form on cold surfaces?
16. Can you name a gas that can easily condense into a liquid?
17. What happens to the pressure of a gas when it is cooled?
18. Define the term ‘latent heat’.
19. What is the difference between boiling and evaporation?
20. How do you know when water is boiling?

Hard Level Questions

1. Explain the concept of latent heat during phase changes.
2. How does the energy change during a substance going from gas to solid?
3. Describe the particle arrangement of a gas at high temperature compared to low temperature.
4. Why is sublimation considered a unique change of state?
5. How does atmospheric pressure affect the boiling point of water?
6. Explain how water can exist in all three states in nature.
7. What role does temperature play in the changes of state for substances?
8. Discuss the energy changes involved in melting and freezing.
9. How does the concept of kinetic energy relate to changes of state?
10. Why does dry ice sublimate at room temperature?
11. What happens at the molecular level when a substance condenses?
12. Explain the importance of changes of state in weather patterns.
13. Describe how you could demonstrate sublimation in a lab setting.
14. Why does frost form on grass on cold mornings?
15. Discuss the relationship between temperature and kinetic energy for different states of matter.
16. Explain why liquids do not have a fixed shape but have a fixed volume.
17. How does the process of evaporation lead to cooling in a liquid?
18. Discuss one industrial application of changes of state.
19. How can changes of state be used to separate mixtures?
20. Explain how the changes of state are involved in the water cycle.

Answers and Explanations

Easy Level Answers

1. Solid
2. It turns into a liquid.
3. Evaporation
4. Freezing
5. Solid
6. Dry ice turning into gas.
7. They gain energy and move apart.
8. Gas turning into liquid.
9. Deposition
10. Water
11. It remains constant.
12. Gases take the shape of their container; liquids do not.
13. Absorb energy
14. Gas
15. Condensation
16. It evaporates.
17. Water vapour
18. 0°C
19. They slow down and come closer together.
20. It turns into gas.

Medium Level Answers

1. It absorbs energy.
2. The energy goes into breaking the bonds, not increasing temperature.
3. When water vapour turns directly into ice.
4. The particles move closer together and vibrate.
5. It expands.
6. Because particles are far apart and move freely.
7. Dew forming on glass.
8. Fastest in gas.
9. Higher pressure raises boiling point.
10. It measures temperature changes based on state.
11. Because it doesn’t change the substance.
12. They slow down and become more ordered.
13. It turns directly into gas from solid.
14. It absorbs heat from the surroundings.
15. Because it’s colder than the air.
16. Water vapour.
17. It decreases.
18. The heat required for a change of state.
19. Boiling is rapid; evaporation is slow.
20. When bubbles form.

Hard Level Answers

1. Latent heat is the energy required to change state without changing temperature.
2. The substance loses energy.
3. Particles are far apart and move quickly at high temperatures; closer together and slower at low temperatures.
4. Because it skips the liquid phase.
5. Higher pressure increases boiling point; lower pressure decreases it.
6. Ice, liquid water, and water vapour.
7. It determines how quickly a substance will change states.
8. Melting absorbs energy; freezing releases energy.
9. Higher kinetic energy means faster-moving particles, affecting state.
10. Because it sublimates at temperatures above -78°C in normal conditions.
11. Molecules lose energy and get closer.
12. Changes of state are crucial for rain, snow, and evaporation.
13. By heating dry ice and observing gas production.
14. Because the air is cooler than the ground.
15. Higher temperature means more kinetic energy leads to faster movement.
16. Liquids have fixed volume due to particle attraction.
17. It causes particles to escape into the air.
18. Distillation is an example.
19. By heating and cooling.
20. The water cycle shows changes from evaporation to condensation.

This concludes our overview of changes of state! Make sure to review these concepts and practice the questions to reinforce your understanding.