Problem Set 2, Chem. 481-881 9-11-2015 Use the following set of bond energies, i

Question

Problem Set 2, Chem. 481-881 9-11-2015 Use the following set of bond energies, in KJ/mole -H 436 (1) The first exercise is to calculate 11gm (in kcal-1 C (food calorie) for palmitic Acid, C1sH3I-COOH, a saturated fatty acid, when it is converted to CO2 and H20, reacting with oxygen.. (The traditional "short hand" value for saturated fats in the diet corresponds to 9C/gm)- Compare your value. (2) For carbohydrates, similarly, consider glucose, an aldehyde Co H120s reacting with oxygen, traditionally given the value of 4 C/gm. (3) For a protein, we have to consider some "average" amino acid, which I write below as being the unit between the 2 lines, and with R = C4H9 a saturated linear hydrocarbon. This is clearly an approximation because there are a large variety of C groups, yet the alkanes on the average predominate. Again, the average value generally quoted is also 4 C/gm. Compare your result using these simple average bond energies, which of course neglect any phase changes involved in the reactants.

Explanation / Answer

You have not provided value of O-H bond which is 458.9 KJ/mol

C6H12O6 +   6O2    ---> 6CO2   + 6H2O

Total bond on product side = 12 (C=O) + 12(O-H)
    = 12 * 736 + 12*458.9
    =14338.8 KJ/mol

Total bond on reactant side = 7 (C-H) + 5(O-H) + 1*(C=O)
    = 7 * 414 + 5*458.9 + 1*736
    =5928.5 KJ/mol

Enerfy released = 14338.8 - 5928.5
                                    = 8410.3 KJ/mol

1 J = 0.239 cal
So, energy released = 8410.3*0.239   = 2010.1 Kcal/mol

Molar mass of C6H12O6 = 6*12+12*1 + 6*16   = 180 gm

Enrgy released per gm = 2010.1/180 kcal/g = 11.2 Kcal/gm = 11.2 C/gm

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