1. Bond Energy and Reaction Energy

2. Units for Measuring Heat
The Joule is the SI system unit for measuring heat:
The calorie is the heat required to raise the temperature of 1 gram of water by 1 Celsius degree

3. - Reaction Energy = Bond Breaking always requires energy
Bond Making always releases energy
Energy
needed
to break
bonds
Energy
released
by bonds
forming H
Reaction
Energy = -

4. Table of Bond Energies

5. Example – Formation of Water
2H O2  H2O 
Bonds broken
Bonds formed
2 H-H 2(432 kJ)
4 O-H 4(467 kJ)
1 O=O 1(498 kJ)
1362 kJ invested
1868 kJ produced
H = 1362 kJ – 1868 kJ = -506 kJ

6. Exothermic Processes
Processes in which energy is released as it proceeds, and surroundings become warmer
Reactants  Products + energy

7. Endothermic Processes
Processes in which energy is absorbed as it proceeds, and surroundings become colder
Reactants + energy  Products

8. Calorimetry – Measuring Energy Change
The amount of heat absorbed or released during a physical or chemical change can be measured, usually by the change in temperature of a known quantity of water in a calorimeter.