Condensation
Evaporation and Condensation: Condensation
Condensation
Condensation
What you'll learn
- Condensation is when a gas (water vapour) turns back into a liquid, usually when it touches or meets something cool.
- Condensation is the opposite of evaporation (liquid to gas).
- Everyday examples: dew on grass in the morning, water droplets on a cold glass, misty bathroom mirrors, clouds forming in the sky.
- To connect condensation with the water cycle, where it forms clouds from evaporated water vapour.
Key concepts
Level 1 — What is condensation?
Verbal: Warm water vapour in the air loses energy when it meets a cool surface, turning back into tiny liquid water droplets.
Symbolic: Gas (vapour) → Liquid (droplets), triggered by cooling.
| Situation | What happens | Everyday example |
|---|---|---|
| Cold drink glass | Water vapour in air touches cool glass and turns to droplets | Water droplets on the outside of a cold glass |
| Morning grass | Cool night air makes water vapour condense | Dew drops on grass |
| Bathroom mirror | Warm shower vapour meets cool mirror | Misty/foggy mirror |
| Sky | Rising warm vapour cools at height | Clouds form |
Everyday link: Why your cold glass of juice gets "wet" on the outside on a warm day.
Level 2 — Condensation and temperature
Verbal: The bigger the temperature difference between the warm, moist air and the cool surface, the more visible and faster the condensation.
Real-life: A glass of ice-cold water on a hot, humid day gets covered in droplets much faster than a glass of cool water on a cold, dry day.
| Condition | Amount of condensation |
|---|---|
| Very cold surface + warm humid air | A lot of condensation, quickly |
| Mildly cool surface + dry air | Little or no visible condensation |
| Warm surface + any air | No condensation |
Worked example
Why does a bottle of cold water "sweat" (get wet outside) when left on a table on a warm day?
Step 1 — Warm air near the bottle contains invisible water vapour.
Step 2 — The vapour touches the cold bottle surface and loses heat energy.
Step 3 — Cooled vapour turns back into tiny liquid water droplets.
Answer: Water vapour from the air condenses into liquid droplets on the cold bottle surface.
Why does a bathroom mirror turn misty during a hot shower?
Step 1 — Hot shower water evaporates, filling the air with warm vapour.
Step 2 — This vapour touches the cooler mirror surface.
Answer: The vapour condenses into tiny droplets, making the mirror look misty.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| The glass "leaks" water from inside | Not seeing the invisible vapour in air | The droplets come from air vapour condensing outside, not leaking through the glass |
| Condensation and evaporation are the same | Confusing the direction of change | Evaporation is liquid to gas; condensation is gas to liquid — opposites |
| Condensation only happens in bathrooms | Limited examples | Condensation also forms dew, clouds, and fog outdoors |
| Cold air always causes condensation by itself | Missing the vapour requirement | Condensation needs water vapour present in the air to begin with |
Quick check
- Define condensation in your own words.
- Give two everyday examples of condensation.
- Why do water droplets form on a cold glass of juice?
- Stretch: Why might condensation on a window be more common on a cold winter morning than a warm summer afternoon?
Revision tip: Take a cold bottle out of the fridge on a warm day and observe how quickly droplets appear outside.
Open the Practice tab for graded questions on Condensation.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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