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H = u + pv

  1. Oct 5, 2008 #1
    So the equation

    [tex]\Delta H = \Delta U + \Delta (PV)


    I know you can transform this equation into the form

    [tex]\Delta H = \Delta U + \Delta (nRT)


    I commonly see the previous equation transfered in to the following

    [tex]\Delta H = \Delta U + \Delta n(RT)

    What I want to know is.. can you transform it into

    [tex]\Delta H = \Delta U + nR \Delta T
  2. jcsd
  3. Oct 6, 2008 #2
    I'd say so. But only if n is constant. What are you trying to do?
  4. Oct 6, 2008 #3
    It was really in relation to this problem

    Calculate the values of delta U, delta S, and delta H for the following process

    1 mole of liquid water at 25 c and 1 atm to 1 mole of steam at 100 c and 1 atm

    I figured out the delta H for the entire process.

    then I tried to figure out delta U from delta H using the relationship

    delta H = delta U + delta (nRT)

    See the thing is... delta H I figured out is for the entire process (temperature rise and state change) and I forget about that.. so I was tryign to get the equation into the form

    delta H = delta U + n x delta T x R

    but that isn't right since delta H already included the delta T variable. and n is really delta n = 1 since I generated 1 mole of gas.

    so yeah all I had to do was times it by T to the right answer
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