1. Endothermic and Exothermic Reactions
Objective 4.02

2. Endothermic Reactions
Require an input of energy – products have more energy than the reactants
Melting a substance
Boiling a substance
Decomposition
Synthesis Reactions

3. Exothermic Reactions
Release (emit) energy – reactants have more energy than products
Condensing a substance
Freezing a substance
Combustion Reactions
Synthesis Reactions

4. Endothermic Reaction Pathway

5. Exothermic Reaction Pathway

6. Heat of Reactions The amount of energy gained or lost in a reaction
2H2 + O2  2H2O kJ
– exothermic
2H2O kJ  2H2 + O2
- endothermic

7. Calculating Enthalpy Enthalpy – the heat energy in a “system”
Measure as “Change in Enthalpy” – ΔH
The energy lost or gained in a reaction
Pg 516 and 517

8. Activation Energy
The energy required to transform the reactants into an activated complex
Pg 534
Activation Energy = Ea
Change in Energy = ΔE

9. Rate Influencing Factors
Nature of Reactants
Surface Area
Temperature
Concentration
Catalyst
Lowers energy of activation – speeds up reaction without being consumed.