Estimate δh for the reaction using bond dissociation energies from table 7.1. give your answer in kcal. c6h12o6 has five c−c bonds, seven c−h bonds, seven c−o bonds, and five o−h bonds.

The equation for the photosynthesis reaction in which carbon dioxide and water react to form glucose is . The hear reaction is the difference between the bond dissociation energies in the products and the bond dissociation energies of the reactants

The reactant molecules have 12 C = O, 12 H - O bonds while the product molecules have 5 C - C, 7 C – O, 5 H – O, and 6 O = O bonds. The average bond dissociation energies for the bonds involved in the reaction are 191 for C = O, 112 for H – O, 83 C –C, 99 C – H, 86 C – O, 119 O = O.

Substitute the average bond dissociation energies in the equation for and calculate as follows

= [12 (C=O) + 12 (H-O)] – [5(C-C) + 7(C-H) + 7 (C-O) + 5(H-O) + 6(O=O)]

= [12x191 kcal/mol + 12x112 kcal//mol] – [5x83 kcal/mol + 7x99 kcal/mol + 7x86 kcal/mol + 5x112 kcal/mol + 6x119 kcal/mol]

= 3636 kcal/mol – 2984 kcal/mol = 652 kcal/mol x 4.184 Kj/1kcal = 2.73x10^3 kJ/mol

So, enthalpy change for the reaction is 652 kcal/mol or 2.73x10^3 kJ/mol

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