Question

Sucrose (C₁₂H₂₂O₁₁, table sugar) is oxidized in the body by O₂ via a complex set of reactions that ultimately produces CO₂(g) and H₂O(l) and releases 5.16 × 10³ kJ of heat per mole of sucrose.

(a) Write a balanced thermochemical equation for this reaction. Include the physical state of each reactant and product.

Enter your answer for ΔH_rxn in scientific notation.

(b) Calculate the energy change per gram of sucrose for this combustion reaction.

kJ/g

Answer 1

(a). Balanced thermochemical equation for this reaction is :

C₁₂H₂₂O₁₁(s) + 12 O₂(g) --------------> 12 CO₂(g) + 11 H₂O (l) ,  ΔH_rxn = - 5.16 × 10³ kJ

(b).

For the combustion of 1 mole of C₁₂H₂₂O₁₁ , heat released = 5.16 x 10³ KJ

Now, Mass of 1 mole of C₁₂H₂₂O₁₁ = Number of moles x Gram molar mass = 1 mol x 342.3 g/mol = 342.3 g

Now, for the combustion of 342.3 g i.e. 1 mole of C₁₂H₂₂O₁₁ ,heat released = 5.16 x 10³ KJ

and

For the combustion of 1g of C₁₂H₂₂O₁₁ , heat released = 5.16 x 10³ KJ x 1g / 342.3 g = 15.07 KJ

Hence, Energy change per gram of sucrose for this combustion reaction = -15.07 KJ/g