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Hess' law help

  1. Feb 29, 2016 #1
    1. The problem statement, all variables and given/known data
    1. (a) From the following data, 2 Cu (s) + S (s) Cu2S (g) ∆rH° = - 79.5 kJ mol-1 S (s) + O2(g) SO2 (g) ∆rH° = - 296.8 kJ mol-1 Cu2S (s) + 2 O2(g) 2CuO (s) + SO2(g) ∆rH° = - 527.5 kJ mol-1 Determine ∆rH° for Cu(s) + ½ O2 (g) CuO (s) at 298 K

    (b) Given the following Cp / (J K-1 mol-1) Cu(s) = 24.44 O2(g) = 29.36 CuO (s) = 42.30 Calculate the ∆rH° for the reaction at 1000K.

    2. Relevant equations

    More so part b is it correct
    3. The attempt at a solution
    2 Cu (s) + S (s) ---> Cu2S (g) ∆rH° = - 79.5 kJ mol-1
    SO2 (g) ---> S (s) + O2(g) ∆rH° = +296.8 kJ mol-1
    Cu2S (s) + 2 O2(g) ---> 2CuO (s) + SO2(g) ∆rH° = - 527.5 kJ mol-1

    Adding the above three equations results in this:

    2 Cu (s) + O2(g) ---> 2CuO (s) ∆rH° = -310.2 kJ

    Dividing through by 2 = -155.1 kJ.
    part b cu(s) =+79.5 =24.4 (1000-298 k) using the equation ∆rHT2=∆rHT1+∆CP(T2-T1)
    SAME GOES FOR O2 and CUO ?
     
  2. jcsd
  3. Mar 2, 2016 #2
    How did you get the last equation? ΔH(T1)=ΔH(T2) + CpΔT ?
     
  4. Mar 2, 2016 #3
    actually i got Δcp= cp products -reactants= 43.3-24.44+0.5*29.36)= 3.18 kj/mol
    ΔHr 1000= ΔHr 298+ΔCpΔT
    -155.1*10^3 J-MOL * 3.18 JK-MOL *702 K
    =-155.1 *10^3 + 2232.36
    = 152.9 KJ/MOL
     
  5. Mar 2, 2016 #4
    And the equation was my lecture notes
     
  6. Mar 2, 2016 #5
    actually i got Δcp= cp products -reactants= 43.3-24.44+0.5*29.36)= 3.18 kj/mol
    ΔHr 1000= ΔHr 298+ΔCpΔT
    -155.1*10^3 J-MOL * 3.18 JK-MOL *702 K
    =-155.1 *10^3 + 2232.36
    = 152.9 KJ/MOL
     
  7. Mar 3, 2016 #6
    Check the equation once again. It is dimensionally incorrect.

    Cp has units J K-1 mol-1 while ΔH has units J mole-1
     
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