Thermochemistry
Calculating heat of reaction from bomb calorimetry data
A student runs two experiments with a constant-volume "bomb" calorimeter containing 1500. g of water (see sketch at
right).
First, a 6.500 g tablet of benzoic acid ($C_6H_5CO_2H$) is put into the "bomb" and burned completely in an excess of
oxygen. (Benzoic acid is known to have a heat of combustion of 26.454 kJ/g.) The temperature of the water is
observed to rise from 12.00 °C to 35.88 °C over a time of 10.1 minutes.
Next, 5.730 g of ethane ($C_2H_6$) are put into the "bomb" and similarly completely burned in an excess of oxygen. This
time the temperature of the water rises from 12.00 °C to 46.03 °C.
Use this information, and any other information you need from the ALEKS Data resource, to answer the questions
below about this reaction:
$2C_2H_6(g) + 7O_2(g) \rightarrow 4CO_2(g) + 6H_2O(g)$
Be sure any of your answers that are calculated from measured data are rounded to the correct number of significant digits.
Note for advanced students: it's possible the student did not do these experiments sufficiently carefully, and the values you calculate may not exactly match
published values for this reaction.
Is this reaction exothermic, endothermic, or neither?
If you said the reaction was exothermic or endothermic, calculate the amount of heat that was
released or absorbed by the reaction in the second experiment.
Calculate the reaction enthalpy $\Delta H_{rxn}$ per mole of $CO_2$.
