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Standard enthalpy of formation

  1. Jan 16, 2017 #1
    So when they said that to produce water vapor at standard state it releases -241 KJ/mol
    and liquid water -284 KJ/mol

    You can't create water vapor at standard temperature but I assume they used Hess' law
    Anyway, my question is when you change from water to vapor you need 44KJ/mol

    So that would be the energy required to change from 25 C liquid to 25 C vapor.
    Does it change for example when you want to change it from another temperature?
  2. jcsd
  3. Jan 17, 2017 #2


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    Science Advisor

    Yes. Do you know a formula for the variation of ΔH with temperature?
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