AP Chemistry
6.6 Introduction to Enthalpy of Reaction
6.4 Heat Capacity and Calorimetry
A student determines the standard molar enthalpy of combustion, \(\Delta H_{\text{comb}}^\circ\), of an unknown liquid fuel using a bomb calorimeter. In the calibration trial, the student combusts a sample of benzoic acid (\(\text{C}_7\text{H}_6\text{O}_2\), molar mass \(122\text{ g/mol}\)), which has a known \(\Delta H_{\text{comb}}^\circ = -3.20 \times 10^3\text{ kJ/mol}\). In a second trial, the student combusts a sample of the unknown liquid fuel in the same calorimeter. The experimental data collected are shown in the table below.
Based on the data in the table, what is the value of \(\Delta H_{\text{comb}}^\circ\) for the unknown liquid fuel?
| Measurement | Calibration trial (benzoic acid) | Fuel trial (unknown fuel) |
|---|---|---|
| Molar mass of substance (\(\text{g/mol}\)) | \(122\) | \(46.0\) |
| Mass of sample combusted (\(\text{g}\)) | \(1.22\) | \(0.920\) |
| Initial calorimeter temperature (\(^\circ\text{C}\)) | \(21.50\) | \(22.00\) |
| Final calorimeter temperature (\(^\circ\text{C}\)) | \(25.50\) | \(25.50\) |
Based on the data in the table, what is the value of \(\Delta H_{\text{comb}}^\circ\) for the unknown liquid fuel?
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