1. IV. Reaction Energy (p. 514 - 517)
Ch. 17 – Chemical Reactions
IV. Reaction Energy (p )

2. A. Reaction Pathway Diagram
Sometimes called “Reaction Energy Diagram” or “Reaction Energy Graph”

3. A. Reaction Pathway Diagram
Shows the change in energy during a chemical reaction
Activated
Complex
Products
Reactants

4. A. Reaction Pathway Diagram
Shows the change in energy during a chemical reaction
Activation energy (Ea) =
difference between activated complex energy & reactant energy
Ea:
226 – 100 = 126 J
Change in Enthalpy (DH) =
Eproducts – Ereactants
DH:
= 63 J

5. 2H2(l) + O2(l)  2H2O(g) + energy
B. Exothermic Reaction
A reaction that releases (gives off) energy
products have lower energy than reactants
Energy is a
PRODUCT DH
(energy released)
2H2(l) + O2(l)  2H2O(g) + energy

6. C. Endothermic Reaction
A reaction that absorbs (takes in) energy
reactants have lower energy than products
Energy is a
reactant DH
(energy absorbed)
2Al2O3 + energy  4Al + 3O2

7. A. Reaction Pathway Diagram
Catalyst: speeds up the reaction by lowering the Ea
(catalyzed reaction in red)
The catalyst is not a reactant OR a product. It is written on top of the reaction arrow. I2
Al2O > Al + O2

8. A. Reaction Pathway Diagram
Catalyst: speeds up the reaction by lowering the Ea
(catalyzed reaction in red)
NOTE:
Ereactants,
Eproducts,
& DH are unchanged by a catalyst
Catalyst only affects Ea
Biological Catalysts are called ENZYMES