Find Energy of C=C Bond in Fumaric and Succinic Acid

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Homework Statement

Enthalpies of fumaric and succinic acid are as follows:

Fumaric:
dH(combustion) = -1336kJ/mol
C4H4O4(s) + 3O2 -> 4CO2(g) + 2H2O(l)

Succinic:
dH(combustion) = -1469kJ/mol
C4H6O4(s) + 3.5 O2(g) -> 3H2O(l)

Find the energy of the C=C bond

BE:
H-H: 432 kJ/mol
C-H: 413 kJ/mol
C-C: 347 kJ/mol

dH(formation)
H2O(l): -241.8 kJ/mol
CO2(g): -393.5 kJ/mol

Homework Equations

dH(combustion) ≠ dH(formation)

dH(formation) = sigma(BE reactants) - sigma(BE products) + dH(formation)

The Attempt at a Solution

 

[member 553083]

Fumaric:BE reactants = 2C4H4O4 + 3O2 = 8*413 + 3*(0) = 3304kJ/molBE products = 4CO2 + 2H2O = 4*(-393.5) + 2*(-241.8) = -2183.2kJ/moldH(formation) = 3304 - (-2183.2) + (-1336) = -2035.8kJ/molC=C bond = 8*347 = 2776kJ/molSuccinic:BE reactants = C4H6O4 + 3.5O2 = 4*413 + 3.5*(0) = 1652kJ/molBE products = 3H2O = 3*(-241.8) = -725.4kJ/moldH(formation) = 1652 - (-725.4) + (-1469) = -536.4kJ/molC=C bond = 6*347 = 2082kJ/mol