Question

Calculate the number of moles in 1.00 g of sucrose and of palmitic acid. Enter your answers in the table below. (Hint: n = m/MW).

Molar enthalpy of combustion, DrHo

kJ mol-1

-5645

-9978

Based on the energy released in respiration per gram, which is the more potent fuel source, sugar or fat? Is this consistent with the notion that each new CO bond made via oxidation releases energy?

Answer 1

1 g of sucrose = 1/ molar mass of sucrose = 1/342.2965 = 0.00292 moles = 2.92 x 10^-3 moles 1 g of palmitic acid = 1/ molar mass of palmitic acid = 1/256.4 = 0.0039 moles = 3.9 x 10^-3moles. Molar enthalpy of combustion sucrose = -5645kj/mol. Molar enthalpy of combustion of palmitic acid = -9978kj/mol 1g sucrose release = - 5645 x .0092 = -16.48 kj/g . Based on above calculation , palmitic acid is more potent fuel. Yes, this is consistent with the notion that each new co₂ bond made via oxidation releases