Unit 9 – Reaction Rates and Equilibrium

1. Unit 9 – Reaction Rates and Equilibrium The area of chemistry that concerns reaction rates (how fast a reaction occurs)

2. Collision Model Key Idea: Molecules must collide to react. However, only a small fraction of collisions produces a reaction. Why?

3. Not all “swings” are successful.

4. Why is it not burning? • Activation energy must be supplied (in the form of friction between friction strip and match tip)

5. Collision Model Collisions must have sufficient energy to produce the reaction Must equal or exceed the activation energy. 1.

6. Activation energy B = Activation energy (Highest Point) C = Energy released by reaction A = Energy of reactants D = Energy of products

7. Collision Model Colliding particles must be correctly oriented to one another in order to produce a reaction.

8. HCl with C2H4

9. Reaction rate • A change in concentration of a reactant or product over time • In other words, speed a chemical reaction occurs

10. Factors Affecting Rate 1. Temperature As temperature INCREASES , reaction rate INCREASES. Because… • Particles collide more FREQUENTLY • Particles collide more ENERGETICALLY 2. Surface areaas the surface area INCREASES, reaction rate INCREASES. 3. Concentration As the concentration INCREASES, reaction rate USUALLY INCREASES. 4. Presence of Catalysts, which lower the activation energy by providing alternate pathways

11. Collision Model Remember… Collisions must have sufficient energy AND a correct orientationto produce a reaction Increasing temp, concentration, or particle size contributes to more energy and/or more chances at colliding with a correct orientation 1.

12. Effect of temperature – more chances of successful collision

13. Effect of surface area – More chances of successful collision

14. Effect of concentration – More chances of successful collisions

15. CATALYST • A substance that speeds up a reaction without being consumed

16. Lowering of Activation Energy by a Catalyst • * You don’t get more product, you just get it faster

17. Catalysis • Enzymes: A large molecule (usually a protein) that catalyzes biological reactions • Example: Digestion • Substrate (s) ------------------- > product(s)

18. Catalysis • Heterogeneous catalyst: Present in a different phase than the reacting molecules. • Example: Catalytic converters in automobiles • NO (g)  N2 + O2 • CO (g)  CO2 • Fuel + O2 CO2 + H2O * * * * Rh, Pt, metal oxides

19. Catalysis • Homogeneous catalyst: Present in the same phase as the reacting molecules. • Example: “Elephant’s Toothpaste” • 2 H2O2 (aq) ---- > 2 H2O(l) + O2 (g) • Intermediate steps: • H2O2(aq) + I-(aq) → OI-(aq) + H2O(l) • H2O2(aq) + OI-(aq) → I-(aq) + H2O(l) + O2(g) • I- is not consumed in the reaction. KI