A bomb calorimeter can be used for accurate determination of the heat change during combustion of a fuel - AQA - A-Level Chemistry - Question 5 - 2020 - Paper 3

For octane: We first calculate the heat change:

$\Delta T = 12.2 °C$

Now, using the heat capacity derived:

$q = C_{cal} \Delta T$

Substituting:

$q = 6.52 kJ K^{-1} \cdot 12.2 K = 79.66 kJ$

Now calculating per mole of octane:

$\text{Amount of octane} = \frac{2.00 g}{114.0 g mol^{-1}} = 0.0175 mol$

Thus heat change per mole:

$\text{Heat change per mole} = \frac{79.66 kJ}{0.0175 mol} = 4544.57 kJ mol^{-1}$

The heat change calculated from the bomb calorimeter experiment is not an enthalpy change because it occurs at constant volume, while enthalpy change is defined at constant pressure.

To calculate the percentage uncertainty:

$\text{Percentage uncertainty} = \frac{0.1 °C}{12.2 °C} \times 100 = 0.82 \%$

One change could be to use a larger mass of fuel, which would result in a greater temperature change, thus reducing the percentage uncertainty.