Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: H = u + pv

  1. Oct 5, 2008 #1
    So the equation

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

    [/tex]

    I know you can transform this equation into the form


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

    [/tex]

    I commonly see the previous equation transfered in to the following


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

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

    [tex]\Delta H = \Delta U + nR \Delta T
    [/tex]
     
  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
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook