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Change in internal energy during vapourization of water

  1. Dec 3, 2015 #1
    1. The problem statement, all variables and given/known data
    Assuming water to be an ideal gas, enthalpy of vaporization is x joules per mole. I have to find change in internal energy an 100 degree Celsius for one mole of water. also find heat absorbed.

    2. Relevant equations

    3. The attempt at a solution
    I initially thought that during vaporization of water, temperature does not change and hence internal energy should remain constant (assuming ideal gas behaviour by water ).
    but my assumption was found to be wrong.

    I am totally confused.....
  2. jcsd
  3. Dec 3, 2015 #2


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    It takes energy to accomplish the phase change from liquid to vapor. The fact that this phase change occurs at constant temperature does not necessarily mean that the energy in the water is constant. Same deal when water changes phase from liquid to solid. Energy must be removed from the liquid water to turn it into ice. The energy which must be added/removed is known as latent heat. For freezing water, this is the latent heat of fusion. For making steam, this is the latent heat of vaporization.

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