Question

Kemmi Major does some experimental work on the combustion of sucrose:

C₁₂H₂₂O₁₁(s) + 12 O₂(g) à 12 CO₂(g) + 11 H₂O(g)

She burns a 0.05392 g pellet of sucrose in a bomb calorimeter with excess oxygen. She determines the q_rxn to be –916.6 J for the reaction. Calculate the ∆H value for the combustion reaction. (Round the answer to 3 significant digits, units of kJ, pay attention to positive or negative.)

Answer 1

Mass of Sucrose burnt = 0.05392 gm

Molar mass of sucrose =  342.3 g/mol

Moles of Sucrose = 0.05392 g / 342.3 g/mol = 1.57522 x 10^-4 Moles

Amount of energy released = -916.6 Joules = -0.9166 Kilo joules

Enthalpy (∆H) of reaction is known as amount of energy released when one mole of sucrose is burnt. Since energy is released the negative sign is added in front of the energy.

Enthalpy (∆H) of reaction = -0.9166 Kilo joules / 1.57522 x 10^-4 Moles = -5818.8461 Kilojoules / mole

H value for the combustion reaction is -5818.8461 Kilojoules / mole