Evaporation
Evaporation and Condensation: Evaporation
Evaporation
Evaporation
What you'll learn
- Evaporation is when a liquid slowly turns into a gas (vapour) from its surface, at any temperature — not only at the boiling point.
- Evaporation happens faster with more heat, more wind (moving air), and a larger exposed surface area.
- Everyday examples: wet clothes drying, puddles disappearing after rain, wet floors drying.
- Evaporation is different from boiling — boiling happens fast throughout the liquid only at a fixed high temperature (100 degC for water).
Key concepts
Level 1 — What is evaporation?
Verbal: At the surface of a liquid, some particles have enough energy to escape into the air as vapour, even without reaching the boiling point.
Symbolic: Liquid (surface) → Gas (vapour), slow process, happens at any temperature.
| Situation | What happens | Everyday example |
|---|---|---|
| Wet clothes on a line | Water evaporates into the air | Clothes dry over hours |
| Puddle after rain | Water slowly evaporates | Puddle disappears by evening |
| Wet floor | Water evaporates from the surface | Floor dries after mopping |
Everyday link: Why wet hair dries faster in front of a fan.
Level 2 — What speeds up evaporation?
Verbal: Evaporation speeds up with heat (more energy for particles to escape), wind (carries vapour away, making room for more), and larger surface area (more particles exposed to air at once).
Real-life: Clothes dry faster on a hot, windy day than on a cool, still day; spreading clothes out dries them faster than bunching them up.
| Factor | Effect on evaporation speed |
|---|---|
| Higher temperature | Faster evaporation |
| More wind/air movement | Faster evaporation |
| Larger surface area | Faster evaporation |
| Higher humidity (already wet air) | Slower evaporation |
Worked example
Why does a wet handkerchief spread out on a chair dry faster than the same handkerchief folded into a small ball?
Step 1 — Spreading it out increases the surface area exposed to air.
Step 2 — More surface area means more water particles can escape into the air at once.
Answer: The spread-out handkerchief dries faster due to greater surface area for evaporation.
Why does a puddle dry up faster on a hot, windy day than on a cool, still day?
Step 1 — Heat gives water particles more energy to escape as vapour.
Step 2 — Wind carries the vapour away, allowing more water to evaporate continuously.
Answer: Heat and wind together speed up evaporation, drying the puddle faster.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Evaporation only happens at boiling point | Confusing with boiling | Evaporation happens at any temperature, but faster when hotter |
| Evaporation is instant | Not observing carefully | Evaporation is usually a slow, gradual process |
| Wind does not affect drying | Overlooking air movement | Wind carries away vapour, speeding up evaporation |
| Evaporated water disappears forever | Missing the water cycle link | Evaporated water becomes vapour in air and later returns as rain |
Quick check
- Define evaporation in your own words.
- Name two factors that speed up evaporation.
- Why do wet clothes dry faster on a sunny, windy day?
- Stretch: Would a covered pan of water evaporate faster or slower than an uncovered pan? Why?
Revision tip: Wet two cloths — spread one out, ball up the other — and time how long each takes to dry.
Open the Practice tab for graded questions on Evaporation.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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