2015 Oct

Principle OF Calorimetry

October 22, 2015

Calorimetry Physics

The principle of calorimetry is to make a quantifiable measurement of the amount heat energy transferred in a system and its relation to temperature. The principle of calorimetry departs from the classical view point that heat is composed of a fluid called “caloric” which flows from a relatively hotter body to the colder body. The idea that heat energy is a measurement of change in temperature of the body was evolved at a much later time after a series of experiments were conducted using instruments called calorimeters.

It is through such experiments that we began to understand that heat energy transferred (both absorbed/released) is directly proportional to the mass of the body and the change in temperature in the body. The proportionality constant is called the specific heat of the substance measured in calories. For example, one calorie is defined as the amount of energy required to increase the temperature of one gram of water by one degree centigrade. In almost all the edible items we purchase, the amount of energy contained in the item is always mentioned. It is the amount of energy generated in the body that is often stored in a chemical form called ATP. The specific heat for water is 4.18 Jg-1K-1.

Another interesting aspect of heat transfer taught in physics tuition classes is that every exchange of heat need not necessarily cause a change in temperature of the substance. When water at 100 oC is provided further energy, one does not find a change in the temperature of the water but the water at 100 oC is converted into steam at 100 oC. This process is called phase transition. The water keeps absorbing energy while it is transformed into steam at the same temperature. This energy is called Latent heat of vaporization. This heat energy is proportional to the mass of the substance and is independent of the temperature. The proportionality constant is called the specific latent heat of the substance. In the case of water if energy is being lost, water at 0 oC is converted into ice at 0 oC. The energy required for this transition to occur is called the Latent heat of fusion and the proportionality constant is called the specific latent heat of ice.

Similarly, the measurements using the principle of calorimetry explain a lot of important phenomenon in thermodynamics. One classical phenomenon that can be explained using this theory is how the clay pots used as an everyday house item works. The clay pots use the heat energy from its surroundings to cool the contents inside. Clay pots are usually porous, the heat from outside evaporates small quantities of water through the pores. This small reduction in the mass of its contents causes the clay pot as a system to loose energy and hence cooling the water inside. It is an indigenous invention made by our ancestors before any phenomenon of heat transfer was remotely understood. A consolidated effort in understanding the phenomenon of heat transfer has also been applied in the field of architecture where open brick and mud structures are used to naturally cool the house.

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