Measuring heat changes Section 11.2

After reading Section 11.2, you should know: How to write or interpret a thermochemical equation How to calculate heat changes in a chemical or physical process

Calorimetry Calorimetry – the accurate and precise measurement of heat changes which occur during chemical and physical processes.

Enthalpy Enthalpy (H) – measure of the heat content of a system. ∆H – change in enthalpy at constant pressure For reactions which take place at constant pressure, the terms heat and enthalpy are used interchangeably, that is, q = ∆H. q = ∆H = (m)(Cp)(∆T)

Calorimeters Coffee cup calorimeter – an insulated device used to measure the absorption or release of heat of a reaction at constant pressure. Bomb calorimeter – used for measuring heat released when a compound is burned at constant volume.

Thermochemical Equations Thermochemical equation – an equation which includes the heat of the reaction The physical state of all reactants and products must also be stated The energy absorbed or released in a chemical equation can be expressed in two different ways: As a reactant or product or Using the symbol ΔH

Thermochemical Equations Endothermic reaction (heat is a absorbed, so it is a reactant): 2 NaHCO3(s) + 129 kJ → Na2CO3(s) + CO2(g) + H2O(g) OR 2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) ∆H = +129 kJ

Thermochemical Equations Exothermic reaction (heat is given off, so it is a product): CaO(s) + H2O(l) → Ca(OH)2(s) + 65.2 kJ OR CaO(s) + H2O(l) → Ca(OH)2(s) ∆H = − 65.2 kJ

After reading Section 11.2, you should know: How to write or interpret a thermochemical equation How to calculate heat changes in a chemical or physical process