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Homework Help: Liquid and vapour in equilibrium

  1. Jul 12, 2017 #1
    1. The problem statement, all variables and given/known data
    A liquid is in equilibrium with its vapour at it’s boiling point. On the average, the molecules in the two phases have equal;; provided options are:
    a. inter-molecule forces
    b.potential energy
    c .Kinetic energy
    d.total energy


    2. Relevant equations

    3. The attempt at a solution:
    Answer is Total energy
    I am unable to understand that since vapour and liquid phases are in equilibrium that means they are exerting similar pressure which means kinetic energy should be same also how can both of them have same energy if they are in different phases???
    Can you please tell me how can total energy be same in this question
  2. jcsd
  3. Jul 12, 2017 #2


    User Avatar
    Science Advisor

    It can't. You have to put energy into a liquid to evaporate it.
    What is the same between two phases in equilibrium? How is this related to any of the options you are given?
  4. Jul 14, 2017 #3
    The question asks for what kind of force / energy can be possibly similar in liquid and vapour phase of the atom/molecule in state of equilibrium.
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