People working in chemistry or related fields use calorimeters to study chemical and other reactions. A calorimeter measures heat given off or absorbed by reactions. If you know a reaction’s heat, you know its energy.
A calorimeter is a container with two chambers. The first chamber holds the reaction you want to measure. The second chamber has a measured volume of water. These two chambers are separated by a metal wall that conducts the heat from the reaction to the water without letting the water mix in. They are both insulated so the heat stays inside the calorimeter as much as possible. A thermometer measures the temperature of the water. The calorimeter’s sealed around the thermometer to prevent heat and water from escaping.
To use the calorimeter, a scientist will put a precisely known amount of pure water into the water chamber. The amount will vary, but 100 milliliters (mL) is typical. She then reads and records the temperature of the water. Then she measures out a precise amount of chemicals she wants to study, puts them in the reaction chamber, and closes the lid. She watches the thermometer very closely for changes in the temperature. As the chemical reaction progresses, the temperature will go up or down. If it goes up, it will reach a peak value, then decline. The opposite’s true if the temperature goes down. It’s important to note the maximum or minimum temperature.
Once this temperature’s found, the scientist determines the reaction’s energy by subtracting the initial temperature from the final, then multiplying by the amount of water used, in this case, 100 mL. If the initial temperature is 24 degrees C and the final is 26 degrees C, we get ( 26 – 24 ) x 100 = 200 calories. Since the temperature went up, we call this an exothermic reaction, giving off heat. If the temperature went down, we’d call that an endothermic reaction, absorbing heat.
Role of Water
Water is the key to making the calorimeter work. The definition for the calorie was set down as the amount of energy that raises the temperature of 1 mL of water one degree Celsius. That’s also called water’s specific heat capacity. When water freezes to ice or boils to steam, the specific heat capacity changes. But as long as we’re dealing with liquid water, we can count on the relation.