A bomb calorimeter, or a constant volume calorimeter, is a device often used to

Question

A bomb calorimeter, or a constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods. In an experiment, a 0.5218 g sample of diphenyl phthalate (C_26H_14O_4) is burned completely in a bomb calorimeter The calorimeter is surrounded by 1.087 times 10^3 g of water. During the combustion the temperature increases from 26.93 to 29.71 degree C. The heat capacity of water is 4.184 J g^-1 degree C^-1. The heat capacity of the calorimeter was determined in a previous experiment to be 782.8 J/degree C. Assumuig that no energy is lost to the surroundings, calculate the molar heat of combustion of diphenyl phthalate based on these data. C_26H_14O_4(s) + (43/2) O_2(g) rightarrow 7H_2O(l) + 20 CO_2(g) + Energy Molar heat of Combustion = kJ/mol

Explanation / Answer

Heat absorbed by water = specific heat of water x temp change x mass

             = ( 4.184 J/gK) x ( 29.71-26.93) x 1087 g = 12643.46 J = 12.6435 KJ

Heat absorbed by calorimeter = specific heat x temp change of calorimeter

                                   = 782.8 J/C x ( 29.71-26.93) = 2176.2 J = 2.176 KJ

total heat absorbed   = 12.6435+2.176 = 14.8 KJ

diphenyl phtahalte moles = mass/ Molar mass of it = 0.5218 /318.32 = 0.00163923

Heat of combustion per mole = dH/moles = 14.8 / 0.00163923 = 9028.6 KJ

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