Why in the process of combustion calories are released?

Question

where do calories come from and where are they going?

Answer 1

Energy comes in a variety of forms: light, heat, motion, electricity, and so forth. The energy in food is measured in units of Calories. A Calorie is defined as the quantity of heat it takes to raise the temperature of 1 kg of water 1 degree Celsius. The energy in food is defined in terms of heat because the quantity measured is heat produced upon burning the food. Burning in the presence of oxygen is the process of combustion. Complete combustion results in the production of energy as well as carbon dioxide and water. Look for evidence of these products during your discovery session.


Food often is labeled with the number of available Calories per gram of food. In this discovery session, you will measure the amount of energy in Calories in two types of nuts: peanuts and almonds. The accepted values for these nuts are listed in many Calorie-counting and diet books (5.18 Cal/gram for peanuts and 5.47 Cal/gram for almonds). This energy is converted into a usable form by chemical reactions in the human body. Therefore, the number of equivalent Calories of food that you eat gives an indication of the amount of energy you will have at your disposal.

QUESTION: How are calories measured?



ANSWER: The caloric value of food is the energy produced by combustion of its proteins, carbohydrates and fats. The amount of energy liberated by the catabolism of food in the body is almost the same as the amount liberated when food is burnt outside the body. The energy liberated by catabolic processes is used for maintaining body functions namely digestion, thermoregulation, muscular contraction and nerve impulses conduction. The amount of energy liberated / unit time is the metabolic rate. When food is burnt outside the body, all the energy is liberated as heat.

The standard unit of heat energy is the calorie (cal), which is defined as the amount of heat energy necessary to raise the temperature of 1 ml of water by one degree, from 15 to 16 celsius at rest.

A slightly different calorie is used in engineering, the international calorie, which equals 1/860 international watt-hour (4.1868 J). A large calorie, or kilocalorie, usually referred to simply as a calorie and sometimes as a kilogram calorie, equals 1,000 calories and is the unit used to express the energy-producing value of food in the calculation of diets.

The energy released by combustion of foodstuffs outside the body can be measured directly and indirectly. In direct calorimetry method the liberated energy can be measured using a bomb calorimeter. It is a metal vessel surrounded by a water insulated container. The food is ignited by an electric spark. The change in the temperature of water is a measure of the calories produced.

In indirect method, the energy production can also be calculated by measuring the amount of oxygen consumed for combustion of food. The amount of oxygen consumed / unit of time is proportionate to the energy liberated. This method of energy estimation is called wet combustion. The caloric value of carbohydrate is 4.1 Kcal /g, protein is 5.65 Kcal/ g and fat is 9.4 Kcal/g.