A bomb calorimeter is used to determine the heat change during the combustion of various alcohols. The calorimeter has a constant volume, meaning it can withstand high pressure changes during the reaction. The calorimeter's heat capacity (CcalC_{\text{cal}}Ccal) must first be calibrated using a compound with a known heat of combustion.
In a calibration experiment, 1.38 g1.38\text{ g}1.38 g of ethanol (Mr=46.0M_r = 46.0Mr=46.0) is completely combusted in excess oxygen inside the calorimeter. A temperature rise (ΔT\Delta TΔT) of 7.6 ∘C7.6\text{ }^\circ\text{C}7.6 ∘C is recorded. Under these experimental conditions, the combustion of 1.00 mol1.00\text{ mol}1.00 mol of ethanol releases 1367 kJ1367\text{ kJ}1367 kJ of energy.
The heat energy released in the calorimeter is given by q=CcalΔTq = C_{\text{cal}}\Delta Tq=CcalΔT. Calculate the heat capacity (CcalC_{\text{cal}}Ccal) of this calorimeter in kJ K−1\text{kJ K}^{-1}kJ K−1. Give your answer to 3 significant figures.
The experiment is repeated under identical conditions using 1.85 g1.85\text{ g}1.85 g of butan-1-ol (Mr=74.0M_r = 74.0Mr=74.0). A temperature rise of 12.2 ∘C12.2\text{ }^\circ\text{C}12.2 ∘C is recorded. Calculate the heat change, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for the combustion of butan-1-ol. If you were unable to calculate a value for CcalC_{\text{cal}}Ccal in Question 1, use 4.80 kJ K−14.80\text{ kJ K}^{-1}4.80 kJ K−1 (note that this is not the correct value). Give your answer to 3 significant figures.
State why the heat change measured in a bomb calorimeter is not defined as an enthalpy change (ΔH\Delta HΔH).
The thermometer used to measure the temperature change of 12.2 ∘C12.2\text{ }^\circ\text{C}12.2 ∘C in Question 2 has an uncertainty of ±0.12 ∘C\pm 0.12\text{ }^\circ\text{C}±0.12 ∘C for each individual reading. Calculate the percentage uncertainty in this temperature change measurement. Suggest one adjustment to the experiment that would decrease this percentage uncertainty without changing the thermometer.