Step out of a pool on a breezy day and you shiver, even in warm air. The water on your skin is carrying off its fastest molecules, and with them the energy that kept you warm. That is evaporation at work.
Evaporation is the escape of the more energetic molecules from the surface of a liquid, at any temperature below boiling. Because the fastest molecules leave, the average energy of those remaining falls, so the liquid cools.
Definition · learn the exact words
Evaporation is the escape of the faster moving molecules from the surface of a liquid; it causes the remaining liquid to cool.
fastest molecules escape → average energy falls → cooling
Evaporation happens only at the surface and at any temperature, unlike boiling.
Section 01
Watch the fast ones leave.
See the most energetic molecules break free from the surface, leaving slower, cooler ones behind.
Stage 1 · Learn
Check evaporation
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Evaporation happens when...
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Evaporation causes the remaining liquid to...
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Compared with boiling, evaporation happens...
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Evaporation is faster when the liquid is...
Section 02
Why it cools, and what speeds it up.
Removing the fastest molecules drains energy from the liquid, and several factors change how quickly this happens.
Only the fast ones escape: the most energetic surface molecules leave, lowering the average energy of those left behind, so the liquid cools.
Any temperature: evaporation happens at the surface at any temperature, not only at the boiling point.
Faster when: the liquid is warmer, the surface area is larger, there is more airflow, or the air is drier.
Examiner trap
Evaporation cools the liquid, it does not warm it. The fastest, highest-energy molecules are the ones that escape, so the average energy of the molecules left behind drops. This is why sweating cools the body.
Stage 2 · Exam
Exam-style questions
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Finish the four checks above to unlock the exam questions
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Sweating cools the body because evaporation...
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Which change would slow down evaporation from a dish of water?
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Evaporation differs from boiling because evaporation...
Skill unlocked
Evaporation, mastered.
That completes the thermal-properties strand. Keep the chain going.
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just evaporation.