Question

Consider the reaction

C12H22O11(s)+12O2(g)→12CO2(g)+11H2O(l)

in which 10.0 g of sucrose, C12H22O11, was burned in a bomb calorimeter with a heat capacity of 7.50 kJ/∘C. The temperature increase inside the calorimeter was found to be 22.0 ∘C. Calculate the change in internal energy, ΔE, for this reaction per mole of sucrose.

Express the change in internal energy in kilojoules per mole to three significant figures.

Hints

ΔE =

  kJ/mol

Answer 1

The heat produced in a bomb calorimeter when combusting a given amount of known substance is the internal energy of the substance combusted

10.0 g of sucrose = (10.0 g of sucrose) / (342.3 g/mol) = 0.02921 moles of sucrose

given that the heat capacity of the calorimeter is 7.50 kJ/ deg C. This means that the temperature of calorimeter increases 1 deg C when 7.50 kJ of heat is absorbed by the calorimeter from the combustion process.

Since the temperature increase was 22.0 deg C when combusting the 0.02921 moles of sucrose, then the combustion process must have given off (22.0 deg C)(7.50 kJ/deg C) = 165.0 kJ

Therefore, the change in internal energy per mole of sucrose combusted would be = (165.0 kJ) / (0.02921 moles of sucrose combusted) = - 5649 kJ/mol .

negative sign indicates that the heat is released when sucrose is combusted.

after rounding off it can be written as -5.65 x 10³ kj