Vapor pressure

  1. Hello,

    This is basic stuff and I feel a bit embarrassed for asking this, but here goes: From what I think I know, evaporation is always happening in a liquid (water, for example) irrespective of the vapor pressure, but boiling only occurs when the vapor pressure is equal or greater than the atmospheric pressure. My question is, how can the molecules escape from the liquid in the former case (evaporation) but are unable to do so in the latter (boiling) until the vapor pressure equals atmospheric pressure?

  2. jcsd
  3. Borek

    Staff: Mentor

    Molecules escape in both cases and it is exactly the same mechanism. The only difference is that during boiling vapor pressure is so high molecules escape the liquid not only on the surface, but even in the bulk, creating bubbles.
    1 person likes this.
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