A researcher studying the nutritional value of a new candy places a 7.00-gram sample of the candy inside a bomb calorimeter and combusts it in excess oxygen. The observed temperature increase is 2.55 °C. If the heat capacity of the calorimeter is 32.00 kJ·K–1, how many nutritional Calories are there per gram of the candy?

Question

aaronq · Answer

$\sf \Delta H_{rxn}=C_p*\Delta T=32.00 ~kJ·K^{–1}*(2.55 °C)=81.6~kJ$

Convert kJ to Cal (i.e. kcal)

$\sf 81.6~kJ*\dfrac{1~Cal}{4.18~kJ}=19.52~Cal$

Per gram: $\sf \dfrac{19.52~Cal}{7~g}=2.79~Cal/g~\approx 2.8~Cal/g$