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Homework Help: Heat enthalpy of molecular hydrogen

  1. Feb 15, 2009 #1
    1. The problem statement, all variables and given/known data
    Look up the enthalpy of formation of atomic hydrogen in the back of the book. This is the enthalpy change when a mole of atomic hydrogen is formed by dissociating 1/2 mole of molecular hydrogen (the more stable state of the element). From this number, determinethe energy needed to dissociate a single H2 molecule , in electron-volts.


    2. Relevant equations
    PV=3100 J
    delta(H)=delta(U)+P*delta(V)
    H=U+PV
    3. The attempt at a solution
    find delta(U)
    delta(U)=delta(H)-P*delta(V)

    found delta(H) to be delta(H)=-217.97 kJ

    According to the standard table T=298 K and P=1 bar=1atm?
    R=8.31 J/K

    PV=RT=(8.31 J/K)(298 K)=2.5 kJ

    H-PV=(-217.97 kJ)-(2.5 kJ)=-220.5 kJ

    Did I find delta(U) correctly?
     
  2. jcsd
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