1. Notes #7
Chapter 18.1
Rates of reaction

2. Rate of a Chemical Change
Rate is the measure of the amount of something changing in a given interval of time. In this case: The amount of reactant changing per unit time.

3. Example:
Rates of chemical reactions: are often measured as a change in the number of moles during an interval of time.

4. Collision Theory
When atoms, ions, or molecules collide with enough kinetic energy, they are able to form products.
The MORE they collide, the more the product will form.

5. Activation Energy
The minimum energy that colliding particles must have in order to react is called the activation energy.

6. There are 4 factors that influence the reaction rate:
1) Temperature: An increase in temperature increases collisions to allow reaction rate to increase.
Storing foods in a
refrigerator keeps them
fresh longer. Low
temperatures slow
microbial action.

7. There are 4 factors that influence the reaction rate:
2) Concentration: higher concentration, more collisions causing an increase reaction rate.
In a room: the more crowded it is, the more you will bump into people.
a. In air, a lighted splint glows and soon goes out.
b. When placed in pure oxygen (higher oxygen concentration), the splint bursts into flame.

8. There are 4 factors that influence the reaction rate:
Particle Size: the more surface area a substance has, the more collisions occur, and the faster it will react.
Pile of little sticks vs Large log
Ways to increase surface area:
Smaller pieces: crushing or mashing
Dissolving into solution

9. There are 4 factors that influence the reaction rate:
4) Catalysts: lowers activation energy. Is a substance added to a reaction that increases reaction rate without being used up.

10. Inhibitors
An inhibitor is a substance that interferes with the action of a catalyst.
Preservatives
Antioxidants and antimicrobials used in drying fruits and preserving fruit juices slow the action of microbes and limit contact with air.

11. Question: Why is it good practice to keep food in closed containers?
Iodine Clock Reaction

12. Reversible Reactions and Equilibrium
Section 18.2
Reversible Reactions and Equilibrium

13. Chemical Equilibrium
At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.
If the rate of the shoppers going up the escalator is equal to the rate of the shoppers going down, then the number of shoppers on each floor remains constant, and there is an equilibrium.

14. SO3 decomposes to SO2 and O2
Chemical Equilibrium
SO3 decomposes to SO2 and O2
SO2 and O2
react to give SO3
At equilibrium, all three types of molecules are present.

15. Chemical Equilibrium
When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium.

16. Factors Affecting Equilibrium: Le Châtelier’s Principle
If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress.
3 Types of Stresses:
1) Changes in concentration of reactants or products
2) Changes in Temperature
3) Change in Pressure

17. Stress 1: Concentration (Of reactants OR products)
See example on board with Mrs. B

18. Stress 2: Temperature
Dinitrogen tetroxide is a colorless gas; nitrogen dioxide is a brown gas. The flask on the left is in a dish of hot water; the flask on the right is in ice.

19. Stress 3: Pressure

20. Practice

21. Next Week: Reaction Rates Lab
Wear closed toes shoes. No back packs in lab.
Equilibrium Constants and Solubility Equilibrium

22. Classwork Due Today
Page 555 # 6
Page 547 #1 ,2, 3, 5