Heat of combustion of food (calorimetry) experiment

Aim: to demonstrate the estimation of the gross energy value of foodstuffs (heat of combustion). Accurate results require great care with the technique.

introduction:

Nutritional labels on the foods people eat provide a great information. One of information included is the caloric content of foods.

You also probably know that if you eat more calories than you expend in metabolic processes and exercise, you will gain weight. If you consume fewer calories than you expend, you will lose weight

However, if you look at the scientific definition of a calorie, you will see it defined as the amount of heat required to raise the temperature of 1.000 g of water from 14.5 °C to 15.5 °C. What does this have to do with food?

from the perspective of a chemical reaction. When chemical bonds break and re-form in a chemical reaction, energy is often absorbed or released.

a calorie is defined, as the amount of heat that is required to raise the temperature of water 1 °C. As we digest and metabolize the food that we eat, bonds are broken and re-formed. These processes release heat that your body can use to fuel other processes that require heat.

Food is oxidized to carbon dioxide and water with an associated release of energy. Fortunately for Humen, cells convert much of this energy into useful work, instead of releasing all of it as heat. Using glucose as an example, nearly half of the energy content of glucose is converted to useful energy in our bodies.

From a specific reactant to a specific product, the same amount of energy will be released (or consumed) regardless of the pathway.

Most of the carbon atoms in a peanut, , will be oxidized to carbon dioxide and water in our bodies- providing a certain number of calories of energy. The same amount of energy is released by burning the peanut to produce these same products. This heat can be used to heat a known mass of water. The temperature change of the water can be used to calculate the amount of energy added to the water. Since the energy added to the water came from the combustion of the peanut, we know how much energy was released from the peanut assuming all of the energy was transferred.

In this experiment, it will be relating the caloric content of foods, specifically peanuts, to the energy required to heat water.

capacity of water in calories and its temperature change to determine the caloric content.

Calorimetry is a technique that is used to determine the heat involved in a chemical reaction. When determining the heat of combustion of a substance or the caloric value of foods, the measurements are often made using a bomb calorimeter.

In this device, the weighed sample is placed in a heavy steel container called a bomb and the atmosphere of the bomb is filled with pure oxygen.
The bomb is then placed in a well insulated container called a calorimeter which has been filled with a measured amount of water. The sample, in the pure oxygen atmosphere, is ignited by an electric spark and the heat generated by the burning sample warms the bomb and the surrounding water. At equilibrium, both the bomb and the water will be at the same temperature.

Using the law of conservation of energy:

Heat evolved by the reaction = Heat absorbed by the water + Heat absorbed by the bomb

or, in equation form:

qreaction = -(qwater + qbomb ) (where q is the symbol for heat)

The qreaction has a negative value because the combustion reaction is exothermic (i.e., it releases energy to the surroundings).

The qwater and the qbomb are calculated from the temperature change of the water and the bomb and the specific heat of the water and the bomb.
The total gives the heat of combustion of the sample that was used.

In this experiment, the energy of a peanut, will be determined using a simplified set-up. The peanut will be burned.