Kim Young, age 16, of Poughkeepsie, N.Y., for her question:

CAN YOU EXPLAIN CALORIMETRY?

Calorimetry is the science of measuring a quantity of heat, which is expressed in calories, as distinct from thermometry, the science of measuring the intensity of heat, which is expressed as temperature.

A calorimeter is the instrument used to measure the amount of heat. One widely used type consists of an insulated container of water, a stirring device and a thermometer. A heat source is placed in the calorimeter, the water is stirred until equilibrium is reached and the rise of temperature is noted by reading the thermometer.

Latent heat, which is not associated with a change in temperature, is the heat evolved or absorbed by a substance as it changes from one state to another, as from liquid to solid or vice versa.

When the heat source is a chemical reaction, such as the burning of a fuel, the reacting substances are placed in a heavy steel vessel called a bomb. The bomb is placed within the calorimeter and the reaction is started by ignition with an electric spark.