Name the required changes of state
Connect melting, freezing, vaporisation and condensation to their starting and finishing states.
Section 2.1.1 · States of matter
Core and Extended; Physics 0625, 2026–2028, section 2.1.1. Distinguish solids, liquids and gases and name the required changes among them. Direct solid-to-gas and gas-to-solid changes are not required in this section. Written practice is self-checked.
Before you begin
- Distinguish solids, liquids and gases.
- Read a directed arrow from its starting state to its end state.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which is the starting state in liquid-to-gas change?
What you will learn
- Name solid–liquid and liquid–gas changes in each direction.
- Distinguish boiling and evaporation as routes from liquid to gas.
Name a change from its direction
Melting is solid to liquid. Freezing, also called solidification, is liquid to solid. Changing a liquid to gas is vaporisation; boiling and evaporation are two ways it occurs. Condensation is gas to liquid. First identify the starting and finishing states, then choose the term; naming a change only from 'getting hotter' can fail when the sample has not changed state.
Ice melting produces liquid water, while liquid water freezing produces ice. Water vapour condensing produces liquid water. A liquid heated but still liquid has undergone a temperature change without the stated change of state. Direct solid-to-gas and gas-to-solid changes are not required by this selected section and are not presented as missing requirements.
Boiling and evaporation share an endpoint
Boiling and evaporation both produce gas from liquid. Evaporation occurs at a liquid surface and can occur below the boiling temperature; boiling forms vapour bubbles within the liquid under the appropriate conditions. You can therefore describe a puddle gradually drying as evaporation even if no bubbles are present. Detailed energy and rate explanations belong to the later melting, boiling and evaporation section.
Gas bubbles in a description require interpretation: bubbles made by an injected gas do not establish that the liquid is boiling. Likewise, visible white mist above hot water contains condensed liquid droplets, while water vapour itself is invisible. Name the process using the supplied start and end states rather than the appearance of every nearby component.
Pause and explain
Water vapour becomes liquid droplets on a cool surface. What is this change?
Worked example
Ice becomes liquid water; a puddle dries without boiling; water vapour becomes liquid droplets. Name each change.
Show the worked solution
- Solid to liquid is melting.
- Surface liquid to gas without boiling is evaporation.
- Gas to liquid is condensation.
Answer Melting; evaporation; condensation.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name solid to liquid, liquid to solid, liquid to gas and gas to liquid in order.
Give me a hint
Read each arrow in its specified direction.
Compare my reasoning
- Solid to liquid is melting; the reverse is freezing or solidification.
- Liquid to gas is vaporisation, through evaporation or boiling.
- Gas to liquid is condensation.
Melting; freezing or solidification; vaporisation; condensation.
Look for these in your work
- Keep all four directions correct.
- Accept the appropriate alternative terms.
Liquid water forms ice, a wet cloth dries without boiling, and invisible water vapour forms liquid droplets. Name each process.
Give me a hint
Use starting and finishing states and the surface-drying description.
Compare my reasoning
- Liquid to ice is freezing.
- Drying without boiling involves evaporation into gas.
- Water vapour to liquid droplets is condensation.
Freezing; evaporation; condensation.
Look for these in your work
- Distinguish drying from freezing.
- Do not call liquid droplets gaseous vapour.
Air is pumped through cool liquid water to make bubbles. A student says the water must be boiling. Explain why that is not established and state what boiling would involve.
Give me a hint
Identify whether the bubbles are injected air or water changing into gas.
Compare my reasoning
- The supplied bubbles come from pumped air.
- This does not show the liquid water changing state.
- Boiling would involve formation of water-vapour bubbles within the liquid under suitable conditions.
Injected air bubbles do not establish boiling of the water.
Look for these in your work
- Use the origin of the bubbles.
- Describe the required state change.
Common mistakes
- Name the direction of the change.
- Heating does not always mean melting or boiling.
- Injected bubbles do not establish boiling.
What can you explain now?
What is another name for freezing?
Compare with the explanation
Solidification.
Both describe a change from liquid to solid.
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Make it stick
Name each required directed change and explain why bubbles or heating alone may be insufficient evidence.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.