Question

The aromatic hydrocarbon cymene (C10H14) is found in nearly 100 spices and fragrances including coriander, anise, and thyme. The complete combustion of 1.608 g of cymene in a bomb calorimeter (Ccalorimeter = 3.640 kJ/°C) produced an increase in temperature of 19.35°C. Calculate the molar enthalpy of combustion of cymene (ΔHcomb) in kilojoules per mole of cymene.

Answer 1

Answer:

5878 kJ/mol

Explanation:

According to the law of conservation of energy, the sum of the heat released by the combustion and the heat absorbed by the calorimeter is zero.

Qcomb + Qcal = 0

Qcomb = -Qcal    [1]

The heat absorbed by the calorimeter (Qcal) can be calculated using the following expression:

Qcal = Ccal . ΔT = 3.640 kJ/°C × 19.35°C = 70.43 kJ

where,

Ccal is the heat capacity of the calorimeter

ΔT is the difference in temperature

From [1],

Qcomb = - 70.43 kJ

Since this heat is measured at constant pressure, the molar enthalpy of combustion of cymene is:

$\Delta Hcomb=\frac{-70.43kJ}{1.608g} .\frac{134.21g}{mol} =5878kJ/mol$