Question

An electrical heater is used to add 18.25 kJ of heat to a constant-volume calorimeter. The temperature of the calorimeter increases by 3.12°C. When 1.75 g of methanol (CH₃OH) is burned in the same calorimeter, the temperature increases by 6.78°C. Calculate the molar heat of combustion for methanol (enter in kJ).

Answer 1

heat capacity of calorimeter (C) = q/DT

                                 = 18.25/3.12

                                 = 5.85 kj/c

no of mol of methanol burned = 1.75/32 = 0.055 mol

heat released(q) = c*DT

                 = 5.85*6.78

       = 39.663 kj

molar heat of combustion for methanol(DHrxn) = -q/n

           = -39.663/0.055

        = -721.14 kj/mol