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The transformation of a liquid into a gas (or vapour) below the boiling point of the liquid

When you heat a liquid – but without reaching its boiling point – it evaporates, and becomes a gas. Here’s the exact process:

  1. As the particles in the liquid are heated, the thermal energy is transferred into kinetic energy – so they start to move around more quickly as the temperature increases.
  2. The fastest moving particles (particles in a liquid have different amounts of energy) overcome the forces of attraction between other particles.
  3. These faster particles escape from the surface of the liquid to form a gas.

How quickly this can happen depends on 3 things:

  1. The temperature of the liquid – the hotter it is, the faster the particles move, on average.
  2. The surface area of the liquid – the larger this is, the more space the fastest moving particles have to escape.
  3. The air flow over the surface of the liquid – the faster the air flow, the more quickly the liquid evaporates.

So now you know why hanging out your washing on a sunny and windy day dries your clothes more quickly!