When a 3.80-g sample of liquid octane (c8h18) is burned in a bomb calorimeter, the temperature of the calorimeter rises by 27.3 °c. the heat capacity of the calorimeter, measured in a separate experiment, is 6.18 kj>°c. determine the δe for octane combustion in units of kj>mol octane?

Answer is: the δe for octane combustion is - 5112.42 kJ/mol.

Chemical reaction: C₈H₁₈ + 25/2O₂ → 8CO₂ + 9H₂O.

m (C₈H₁₈) = 3.80 g; mass of octane.

n (C₈H₁₈) = m (C₈H₁₈) : M (C₈H₁₈).

n (C₈H₁₈) = 3.8 g : 114 g/mol.

n (C₈H₁₈) = 0.033 mol; amount of octane.

cp = 6.18 kJ/°C, specific heat capacity of the bomb calorimeter.

Qcal = ΔT · cp.

Qcal = 27.3°C · 6.18 kJ/°C.

Qcal = 168.71 kJ; amount of heat absorbed.

ΔE = Qcal : n (C₈H₁₈).

ΔE = 168.71 kJ : 0.033 mol.

ΔE = 5112.42 kJ/mol.

Heat released from combustion of octane = heat absorbed by calorimeter = heat capacity * temperature change = 6.18 kJ/C * 27.3 C = 169 kJ

Molar mass of octane = 8 * 12.01 g/mol + 18 * 1.01 g/mol = 114.26 g/mol

Moles octane burned = 3.80 grams * 1 mol / 114.26 grams = 0.0333 mol octane

0.0333 mol octane released 169 kJ of heat, heat of combustion is 169 kJ / 0.0333 mol, or 5080 kJ/mol