If the amount of heat absorbed by a calorimeter is too large to neglect or if we require more accurate results, then we must take into account the heat absorbed both by the solution and by the calorimeter. These easy-to-use “coffee cup” calorimeters allow more heat exchange with the outside environment, and therefore produce less accurate energy values.ġ.33 kJ assume that the calorimeter prevents heat transfer between the solution and its external environment (including the calorimeter itself) and that the specific heat of the solution is the same as that for water General chemistry students often use simple calorimeters constructed from polystyrene cups ( Figure 5.12). This enables the accurate determination of the heat involved in chemical processes, the energy content of foods, and so on. Scientists use well-insulated calorimeters that all but prevent the transfer of heat between the calorimeter and its environment, which effectively limits the “surroundings” to the nonsystem components with the calorimeter (and the calorimeter itself). Her work was important to NASA in their quest for better rocket fuels. During her time at the National Bureau of Standards, research chemist Reatha Clark King performed calorimetric experiments to understand the precise heats of various flourine compounds. The temperature change, along with the specific heat and mass of the solution, can then be used to calculate the amount of heat involved in either case.įigure 5.11 In a calorimetric determination, either (a) an exothermic process occurs and heat, q, is negative, indicating that thermal energy is transferred from the system to its surroundings, or (b) an endothermic process occurs and heat, q, is positive, indicating that thermal energy is transferred from the surroundings to the system.Ĭalorimetry measurements are important in understanding the heat transferred in reactions involving everything from microscopic proteins to massive machines. When an endothermic reaction occurs, the heat required is absorbed from the thermal energy of the solution, which decreases its temperature ( Figure 5.11). For example, when an exothermic reaction occurs in solution in a calorimeter, the heat produced by the reaction is absorbed by the solution, which increases its temperature. 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 (all other matter, including components of the measurement apparatus, that serve to either provide heat to the system or absorb heat from the system).Ī calorimeter is a device used to measure the amount of heat involved in a chemical or physical process.
The temperature change measured by the calorimeter is used to derive the amount of heat transferred by the process under study. To do so, the heat is exchanged with a calibrated object (calorimeter). Calorimetry is used to measure amounts of heat transferred to or from a substance. One technique we can use to measure the amount of heat involved in a chemical or physical process is known as calorimetry.
Calculate and interpret heat and related properties using typical calorimetry data.By the end of this section, you will be able to:
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