Bomb calorimeter

It explains the bomb calorimeter instrumentation

1. Bomb Calorimeter Dr.R.Bhuvaneswari AMCAS, Chennai

2. Bomb Calorimeter Bomb calorimeter is used to measure the changes in a system's internal energy due to a reaction. The basic principle is a chemical reaction heats a quantity of water in an insulated container. The reaction takes place inside a sealed container, called as  bomb.

3. Figure: Bomb Calorimeter

4. Instrumentation The foodstuffs(carbohydrates, fats and protein) on combustion by oxygen produces heat. This amount of heat can be measured in a bomb colorimeter. This instrument used to measure the calorific value of foodstuffs. In this instrument the bomb contain a calorimeter, stirrer, thermometer and ignition box. The energy will be supplied through electric wire and known amount of sample is kept inside the bomb.

5. Instrumentation By using the electrical energy, the energy present inside the food material is completely reduced and converted as heat energy through complete oxidation process. Release of heat energy will increase the temperature of the surrounding water. The temperature should be constant throughout the surrounding water which is maintained with the help of thermometer. By this method the energy present inside the carbohydrate, proteins and fats are analysed .

6. Instrumentation Similar conversion process takes place in every cell of human body. Carbohydrates, fats are completely oxidized in the body to CO 2 and H 2 O but proteins are not completely burned because urea is the end product of protein metabolism. Still contains some energy which is not available to the body. Therefore the energy value of proteins in the body is loss than that obtained in the bomb calorimeter.

7. Formula for heat evolved Formula : The heat evolved by 1g of food can be calculated by the following formula: H = W x (T 2 -T 1 ) ------------------ Kcal/g M x 1000 Where W - Water equivalence M - Amount of food burn in gram T 2 -T 1 - Increase in temperature in C.

8. Bomb Calorimeter Physiological energy value of foods: In utilization of carbohydrates, fats and proteins in the body, certain percentage of the nutrients is lost in digestion and the nitrogen of protein is excreted in urine as urea which still contains some energy value. The average losses in digestion in human subjects have been estimated to be 2.0%for carbohydrates, 5.0 % for fats and 8.0% for proteins.

9. Bomb Calorimeter Physiological energy value of foods: The loss of energy in urea has been estimated to be 1.2 Kcal per gram of protein oxidized. The physiological energy values of foods calculated from the gross energy values after allowing for the losses in digestion and metabolism are as follows: carbohydrates 4.0, fats 9.0, and proteins 4.0.

10. Table: Physiological energy value of carbohydrates, fats, proteins Nutrient Gross energy value(K cal/g) Loss of food energy in digestion (%) Energy available after digestion(Kcal/g) Loss of food energy in metabolism(Kcal/g) Physiological energy value of foods (Kcal/g) Carbohydrates 4.1 2 4.0 nil 4.0 Fats 9.45 5 9.0 nil 9.0 Proteins 5.65 8 5.2 1.2 4.0

11. Bomb Calorimeter Example: Weight of wheat taken = 2g Weight of water in the outside vessel =3000g Water equivalent of the calorimeter = 500g Initial temperature of water( T1) = 24 o C Final temperature of water(T2) =26 o C Rise in temperature(T2-T1) = 2 o C Heat gained by water and calorimeter = 3500 x 2=7000 By converting small scle of calories = 7Kcal 1g of wheat produces =3.5 Kcal Calorific value of 100g of wheat = 350 Kcal.

12. Bomb Calorimeter Gross energy value of Food 1g of carbohydrate yield 4.1 Kcal 1g of Fat yield 9.45 Kcal 1g of protein yield 5.65 Kcal.

13. References Handbook of food and Nutrition by  Dr. M. Swaminathan https://www.britannica.com/technology/calorimeter

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