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Homework Help: Thermodynamics beginner's

  1. Mar 8, 2009 #1
    1. The problem statement, all variables and given/known data

    The combustion of 1 gm of ethyl alcohol C2H5OH in abomb calorimeter evelves 29.62 KJ at 25 degree celsius.Calculate:
    1-the change in internal energy of the system
    2-the heat of combustion
    3-delta H formation of C2H5OH

    delta H Formation of CO2 gas =-393.5 KJ/mole
    delta H Formation of H2O liquid=-285.58 KJ/mole
    c=12 H=1 O=16

    2. Relevant equations

    3. The attempt at a solution
    C2H5OH(s)+3 O2(g)-------2 CO2(g)+3 H2O(l)
    1-Since a bomb calorimeter therefore the system has a constant volume therefore the heat is evolved as change in internal energy=Q(v)
    =-29.62 KJ

    2-The Heat of combustion is the change in internal energy of the system in that case but for 1 mole and since no of moles in the calorimeter =1/46 therefore the heat of combustion=46*-29.62=-1362.52 KJ

    3-Delta H=Delta E +Delta (n)*R*T for the ordinary equation one mole ethyl alcohol
    Delta H=-1362.52+(-1)(8.13)(298)(0.001)=-1364.82 KJ
    Delta H=2*-393.5+3*-288.58-delta h formation of c2h5oh
    there the enthalpy of formation=1434.56 KJ
  2. jcsd
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