University:
High School
Course:
High School Physics
Academic year:

2022
Views:

414

Pages:

1
Author:

Herbsdorfn7k8

Calorimetry – Measuring Heats of Reaction Calorimetry, derived from the Latin calor meaning heat, and the Greek metry meaning to measure, is the science of measuring the amount of heat. All calorimetric techniques are therefore based on the measurement of heat that may be generated (exothermic process) or consumed (endothermic process). There are numerous methods to measure such heat, and since calorimetry's advent in the late 18th century, a large number of techniques have been developed. Initially techniques were based on simple thermometric (temperature measurement) methods. Any process that results in heat being generated and exchanged with the environment is a candidate for a calorimetric study. Hence it is not surprising to discover that calorimetry has a very broad range of applicability, with examples ranging from drug design in the pharmaceutical industry, to quality control of process streams in the chemical industry, and the study of metabolic rates in biological (people included) systems. A calorimeter is a device used to measure heat of reaction (the amount of heat involved in a chemical or physical process). It can be sophisticated and expensive or simple and cheap. In a lot of high school chemistry labs, a styrofoam cup is used as a calorimeter, because it is a container with good insulated walls to prevent heat exchange with the environment. In order to measure heats of reactions, we often enclose reactants in a calorimeter, initiate the reaction, and measure the temperature difference before and after the reaction. The temperature difference enables us to evaluate the heat released in the reaction. To do measure the amount of heat, the heat is exchanged with a calibrated object (calorimeter). The change in temperature of the measuring part of the calorimeter is converted into the amount of heat (since the previous calibration was used to establish its heat capacity). The measurement of heat transfer using this approach requires the definition of a system (the substance or substances undergoing the chemical or physical change) and its surroundings (the other components of the measurement apparatus that serve to either provide heat to the system or absorb heat from the system). For combustion reactions, we often enclose all reactants in an explosive-proof steel container, called the bomb. The bomb is then submerged in water or other liquid that absorbs the heat of reaction. The heat capacitor of the bomb plus other things is then measured using the same technique as other calorimeters. Such an instrument is called a bomb calorimeter.