Calorimetry is simply the measurement of heat released or absorbed by a reaction or process. In other words, when we measure the heat given off when something burns, we are performing calorimetry.
Calorimetry can serve a number of purposes, but the most relevant to your life outside of chemistry class is to determine the Calories found in food products. To do this a food (let’s say for example, a cheese puff) is placed into a sealed container filled with pure oxygen and an igniter. The container is placed inside a larger container filled with water.
The cheese puff is ignited and the heat from the reaction transfers to the water, warming it. By measuring the change in the temperature of the water, and knowing it’s mass, we can calculate the amount of heat the water absorbed, and therefore the amount of heat that the cheese puff released when it burned. This measurement, multiplied by the number of cheese puffs in a serving is the caloric content recorded on the cheese puffs package.
A word of warning about food packaging—the energy content is recorded in Calories, not in calories. For the food industry, the capital “C” means kilo. So when a diet soda says it contains 1 Calorie, it really means that it contains 1000 calories. Of course, that’s still not much because if the average adult eats 2000 Calories a day, that’s actually 2,000,000 calories a day.
Calorimetry, then, measures the heat of a reaction by transferring the heat of that reaction to (or from) water. This can be done when the reaction occurs in a separate container (as described above) or when the reaction runs in the water itself.