Question

A 1.800 g sample of octane, C8H18, was burned in a bomb calorimeter whose total heat capacity is 11.66 kJ/°C. The temperature of the calorimeter plus contents increased from 21.59°C to 29.44°C. What is the heat of combustion per gram of octane? What is the heat of combustion per mole of octane? In a bomb calorimeter (where pressure is NOT constant) what is the heat of reaction equal to?

Answer 1

Heat of combution per gram = heat capacity * change in temperature/1.8 gram

Heat of combution per gram = heat energy Kj/moles of octane

Let heat energy is E
Sice it's combustion it will be exothermic with negative sign

E = 11.66*(29.44-21.59)

      = 11.86*7.85

    = -93.101kj

energy converted to Kj = 93.101/1.8 = -51.7 kj/gm

Energy converted to Kj/mole

no of moles of octane = 1.8/114 = 0.157 mole

                                 = 93.101/0.0157

                                = -5930 Kj/mole