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NRG to raise temp equation question

Discussion in 'DAT Discussions' started by JohnnnyD, Jul 26, 2011.

  1. JohnnnyD

    5+ Year Member

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    When finding the energies needed to increase the temp/change phase of a substance, I know to use the q=mcdeltaT equation to find the energy to raise the temp... but my question is about the equation for energy to change phase.

    Which equation is correct to find the energy to change phase:
    (1) q=m delta H where m is the mass in g
    or
    (2)q=n delta H where n is the number of moles

    Chad says (2), TPR says (1), spraknotes on the internet say (1), other internet sources say (1) and (2)...

    I feel like it should be (1) since the equation for the energy to raise temp uses m instead of n, but I never like to second guess Chad...haha
     
    #1 JohnnnyD, Jul 26, 2011
    Last edited: Jul 26, 2011
  2. needzmoar

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    it depends on the units
     
  3. OP
    OP
    JohnnnyD

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    whoa...overload. haha
     
  4. needzmoar

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    haha..ok maybe I should have been more descriptive.

    For example, the enthalpy of fusion for water is 79.72 cal/g or 6.02 kJ/mol

    you need to cancel out the units in the denominator to get the energy.
     

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