1. Measuring heat changes
Section 11.2

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

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

4. 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)

5. 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.

6. 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

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

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

9. 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