Chemistery

A puddle on the pavement disappears by lunchtime, and it never got anywhere near 100 °C. So if water has to reach 100 °C to become a gas — how did the puddle manage it? The short answer: evaporation happens only at a liquid's surface , at any temperature , as fast-moving molecules escape one at a time. Boiling happens throughout the liquid, only at the boiling point , when bubbles of vapour can form inside it. Both are vaporisation; they just differ in where and when. Quick comparison at a glance Feature Evaporation Boiling Where it happens Surface only Throughout the whole liquid Temperature Any temperature below boiling point Only at the boiling point Speed Slow and gradual Rapid Bubbles? No Yes — vapour bubbles rise and burst Energy source Heat drawn from the surroundings Heat supplied continuously Effect on the liquid Cools it down Temperature stays constant Everyday example A puddle drying; sweat on skin A kettle at full boil ...

Put a thermometer in a pan of melting ice and watch it. You're pouring heat in, and the reading refuses to move off 0 °C until the last ice cube is gone. Where is all that energy going? The short answer: a phase change is a physical change in which a substance moves between solid, liquid and gas — melting, freezing, boiling, condensing, subliming or depositing. During a phase change the temperature stays constant, because the energy goes into breaking the attractions between particles rather than speeding them up. The six phase changes There are three states, so there are six one-way trips between them: Change From → To Everyday example Melting (fusion) Solid → Liquid Ice turning to water Freezing (solidification) Liquid → Solid Water turning to ice Vaporisation (boiling/evaporation) Liquid → Gas Water becoming steam Condensation Gas → Liquid Mist forming on a cold window Sublimation Solid → Gas Dry ice fogging without melting Deposition ...