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Calorimetry measures energy changes in substances and is used in nutritional analysis. Calorimeters measure heat absorbed or released, and calculations require knowledge of a substance’s heat capacity. Calorie content is measured by burning food in a calorimeter bomb, and the energy required to burn it is the same as the calorie content.
At its most basic level, calorimetry is the science of heat absorption and loss. It measures energy changes in a given substance and gives observers and researchers an idea of how much energy is required to break that substance down or to make it change. A chemical process can absorb or release energy, and many times this energy is in the form of heat. Nutritional analysis is one of the most common uses of this information. Food breaks down into energy during digestion and this has a measurable energy cost, but metals and other substances can also degrade, usually when exposed to ambient heat. Knowledge of these circumstances is important for people in engineering and other related trades. Calculations are normally made using a device known as a calorimeter and depending on the nature and specificity needed of the test these can be very simple or quite complex. The key is usually the ability to consistently measure changes in temperature over time.
Basic concept
Calorimetry as a science is somewhat complicated, and understanding its deeper mechanisms usually requires both a solid understanding of basic physics and thermodynamics. From a more basic perspective, however, calculations can be viewed as ways of determining a substance’s intrinsic energy based on the heat it emits or absorbs. Temperature measurements are usually the focus. Observing changes in a substance’s temperature over time can provide measurable information about how much energy it is taking in or giving out.
Because it is important
Most compounds, from hard metals to food substances, contain raw energy, but usually do nothing unless the substance undergoes some sort of change. When things are heated, for example, or exposed to other environmental factors, the latent energy often converts into something measurable. Understanding how substances decompose and the conditions under which this happens is really important for a number of different applications.
How does it work
Scientists typically use instruments known as calorimeters to measure how much heat a reaction absorbs or releases. There are a couple of different types. Many high school science students are familiar with a very basic form of calorimetry conducted in a foam cup; the cup acts as an insulator, and the students use it to measure changes in water temperature over time. The results of this type of experiment can give students a basic understanding of energy measurements, but are usually not accurate enough for more serious endeavors.
More serious calculations usually require more intensive tools. A device known as a bomb calorimeter is a very common example. This piece of equipment typically consists of a steel casing — a “bomb” — that will not change in volume. The reactants are placed inside the bomb and the bomb placed inside another container filled with water. The temperature of the water is then taken and the reaction is allowed to occur, often in the form of an explosion.
Experiment execution
Before the reaction takes place, the substances in the bomb are commonly placed under extreme pressure by the addition of oxygen. Scientists also need to account for the heat capacity of the device before they can determine how much heat is absorbed or released. Thermal capacity is a measure of the amount of heat required to raise the device one degree Celsius. After the reaction, the temperature of the water is measured. Once all these values are known, a scientist can calculate the amount of heat absorbed or lost.
Role in nutritional calculations
Calorie calculations are used in many applications, but particularly with food. Foods all contain a certain calorie content, which is basically a description of how much energy they provide, which in turn makes a statement about how much work a person will need to produce to “burn” or “unload” that intake. Most packaged food manufacturers around the world calculate the calorie content of the products they produce and print this measurement on the package.
In general, a calorie is a measure of heat and represents the amount of heat required to raise the temperature of one gram of pure water by one degree Celsius. The calorie with a capital C commonly found on food packaging is actually a kilocalorie: or 1,000 calories. Some countries do not use calories as a measure of food energy, but describe food energy in terms of joules. There are approximately 4.2 joules in each calorie.
When calorimetry is used to determine the calorie content of food, dehydrated foods are placed in a calorimeter bomb. The food item is then burned to find out how much energy the food has. Therefore, when a person eats an item that has 100 kilocalories (about 4,200 joules), it will take the body 100 kilocalories (about 4,200 joules) to burn it.
