17.2 Measuring and Expressing Enthalpy Changes Summary

SECTION SUMMARY

17.2 Measuring and Expressing Enthalpy Changes Summary:

A calorimeter is a device used to measure the absorption or release of heat in chemical and physical processes. In calorimetry, the heat released by the system is equal to the heat absorbed by its surroundings. Conversely, the heat absorbed by a system is equal to the heat released by its surroundings. For systems at constant pressure, the heat changes that occur are the same as changes in enthalpy, symbolized as H. T measure the enthalpy change for a reaction in aqueous solution, it is necessary to measure the initial or final temperature of the system and the mass of the water in the system. It is true that the sign of H is negative for an exothermic reaction. In endothermic reactions, the potential energy of the products is higher than the potential energy of the reactants.

17.2 Measuring and Expressing Enthalpy Changes Vocabulary Terms:

calorimetry: the precise measurement of heat flow out of a system for chemical and physical processes

calorimeter: an insulated device used to measure the absorption or release of heat in chemical or physical processes

enthalpy, (H): the heat content of a system at constant pressure

thermochemical equation: a chemical equation that includes the enthalpy change

heat of reaction: the enthalpy change for a chemical equation exactly as it is written

heat of combustion: the heat of reaction for the complete burning of one mole of a substance

2NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g) ΔH = 129 kJ an example of heat of combustion

CaO(s) + H2O(l) → Ca(OH)2(s) ΔH = −65.2 kJ an example of exothermic process

The End of the Summary