1. A bomb calorimeter , or constant volume calorimeter, is a device often used t

Question

1. A bomb calorimeter, or constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods.

Since the "bomb" itself can absorb energy, a separate experiment is needed to determine the heat capacity of the calorimeter. This is known as calibrating the calorimeter.

In the laboratory a student burns a 0.714-g sample of -D-fructose(C6H12O6) in a bomb calorimeter containing 1020. g of water. The temperature increases from 25.60 °C to 27.80 °C. The heat capacity of water is 4.184 J g-1°C-1.

The molar heat of combustion is 2810. kJ per mole of -D-fructose.

Calculate the heat capacity of the calorimeter.

heat capacity of calorimeter = ___________ J/°C

2.

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.

3.

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.

Explanation / Answer

Q.1: moles of beta-D-fructose used = mass / molar mass = 0.714 g / 180.15 g/mol = 0.003963 mol

Amount of heat liberated on combustion of 0.003963 mol  beta-D-fructose

= (2810 kJ / mol) x 0.003963 mol = 11.137 kJ = 11137 J

According to law of calorimetry,

Heat liberated by beta-D-fructose = Heat absorbed by H2O + Heat absorbed by calorimeter

=> 11137 J = msdT + Heat absorbed by calorimeter

=> 11137 J = 1020 g x 4.184 J g-1°C-1 x (27.80 - 25.60) °C + Heat absorbed by calorimeter

=>  Heat absorbed by calorimeter = 11137 J - 9389 J

=>  Heat absorbed by calorimeter = 1748 J

=> C x dT = 1748 J

=> C x 2.2 °C = 1748 J

=> C = 1748 J / 2.2 °C = 795 J/°C

Hence heat capacity of calorimeter = = 795 J/°C (answer)

Q.2:

moles of xanthone (C13H8O2)  used = mass / molar mass = 0.4779 g / 196.20 g/mol = 0.00243578 mol

According to law of calorimetry,

Heat liberated by  0.00243578 mol xanthone (C13H8O2) = Heat absorbed by H2O + Heat absorbed by calorimeter

=>Heat liberated by  0.00243578 mol xanthone (C13H8O2) = msdT + CdT

= 1042 g x 4.184 J g-1°C-1 x (26.80 - 23.85)°C + 875.5 J/°C x (26.80 - 23.85)°C

= 12861.2 J + 2582.7 J

= 15444 J

=>Heat liberated by  0.00243578 mol xanthone (C13H8O2) = 15444 J

=> Heat liberated by 1 mol xanthone (C13H8O2) = 15444 J / 0.00243578 mol = 6340433 J = 6340.4 kJ/mol

Hence molar heat of combustion = 6340.4 kJ/mol (answer)

Q.3:

moles of anthracene (C14H10) used = mass / molar mass = 0.4488 g / 178.2 g/mol = 0.0025185 mol

According to law of calorimetry,

Heat liberated by 0.0025185 mol anthracene (C14H10) = Heat absorbed by H2O + Heat absorbed by calorimeter

=>Heat liberated by 0.0025185 mol anthracene (C14H10) = msdT + CdT

= 1148 g x 4.184 J g-1°C-1 x (28.22 - 25.29)°C + 984 J/°C x (28.22 - 25.29)°C

= 16956.6 J

=>Heat liberated by 0.0025185 mol anthracene (C14H10) = 16956.6 J

=> Heat liberated by 1 molanthracene (C14H10) = 16956.6 J / 0.0025185 mol

= 6732813 J = 6732.8 kJ/mol

Hence molar heat of combustion = 6732.8 kJ/mol (answer)

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