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A chemical process may either absorb or release energy, and many times this energy is in the form of heat. Scientists often need to know how much heat is absorbed or released when such a process takes place. The measuring of that heat is known as calorimetry. Calorimetry determines how much heat is absorbed or released by noting the temperature before and after the process. By determining the temperature difference, scientists are then able to calculate how much energy was absorbed or released.
In order to measure the amount of heat a reaction absorbs or releases, a calorimeter is often used. Bomb calorimeters are often used in calorimetry to measure the heat gained or lost in a combustion reaction. This device is made out of a steel casing--a "bomb"--that will not change in volume. The reactants are placed inside of the bomb and the bomb placed inside of another container filled with water. The temperature of the water is then noted, and the reaction, often in the form of an explosion, is allowed to take place.
Before the reaction takes place, the substances in the bomb are commonly placed under extreme pressure by the addition of oxygen. Scientists must also take the heat capacity of the device into account before they can determine how much heat is absorbed or released. The heat capacity is a measurement of how much heat it takes to raise the device one degree Celsius. After the reaction, the temperature of the water is taken. After all these values are known, then a scientist is able to calculate the amount of heat that was absorbed or lost.
Calorimetry is used in many applications but most notably with food. When you look at the packages of many food items, you may see the amount of Calories--in some areas the amount of joules--that item has. A calorie is a measurement of heat and measures how much heat is needed to increase the temperature of one gram of pure water one degree Celsius. The Calories many of us see on the food we eat are actually kilocalories--that is, 1,000 calories. A kilocalorie is commonly denoted from the unit calories by the capital "C," but for clarity, the remainder of this article will use the term "kilocalorie" to denote 1,000 calories.
When calorimetry is used to determine the calorie content of food, the dehydrated food items are placed in a bomb calorimeter. The food item is then combusted in order to find out the amount of energy the food has. Thus, when you eat an item that has 100 kilocalories (about 4,200 joules), it will take 100 kilocalories (about 4,200 joules) for your body to burn it. Some countries do not use calories as their food energy measurement, but rather joules. There are approximately 4.2 joules in every calorie.
I saw a device looking like a scale, which was used to measure the (energy) joules in food. Where can I get one? It will be handy when doing shopping.