If I burn 0.315 moles of hexane (C6H14) in a bomb calorimeter containing 5.65 liters of water, what's the molar heat of combustion of hexane if the water temperature rises 55.4 degrees C? The heat capacity of water is 4.184 J/g degrees C.

Question

aaronq · Answer

first find the heat released by burning the hexane, which is in turn absorbed by the water.

      $-q_{hexane}=q_{water}$

Do so by using the variables for water, in the formula:  $q_{water}=m_{water}*C_p*\Delta T$

At constant pressure q = H    (because this happens in a bomb calorimeter)

so now divide the heat evolved by moles of hexane to find the molar enthalpy $H_{comb}^{\circ}$

      $H_{comb}^{\circ} =\dfrac{H_{comb}^{rxn}}{n_{hexane}}$