Anonymous asked in Science & MathematicsPhysics · 1 decade ago

vapor pressure?

what is vapor pressure? i tried wikipedia but i dont get it... anyone got a simpler explanation?

say, in the context of pumps

3 Answers

  • Anonymous
    1 decade ago
    Favorite Answer

    Whenever you have a liquid at room temperature in an open container, usually some of the molecules at the surface of the liquid have enough energy to escape into the air. The liquid molecules which escape "push" against other molecules in the air. This is true because the escaped molecules will collide with other gas molecules and thereby push them out of the way. The pressure with which the molecules that escaped push against the air is the vapor pressure. Note that since the molecules escaped from the surface of the liquid they are no longer liquid molecules but are now vapor molecules.

    As you increase the temperature of the liquid, the thermal energy of liquid increases and more molecules can escape. This means more molecules are pushing against the air, so the pressure they exert is greater. When the vapor molecules push harder against the air than the air pushes back, all of the liquid molecules escape from the liquid's surface and turn into vapor molecules... in other words, the liquid boils or otherwise evaporates.

    You can also change the pressure with which the air pushes back on the escaping molecules by reducing the air pressure (or putting your sample under reduced pressure... which is what a vacuum pump does).

  • Anonymous
    1 decade ago

    Vapor pressure is the pressure below which some of the liquid evaporates and forms a gas (it doesn't need to boil to do this). For example, if the pressure in part of a pump is too low, the liquid can form gas bubbles, which can reduce the efficiency of the pump. This is called cavitation.

  • 1 decade ago

    Vapor pressure is the pressure exerted by liquid/gas molecules as they try to escape the surface. As temperature increases, vapor pressure will increase. This is due to weakening of intermolecular forces.

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