1. Kinetics and Equilibrium review (Items 114-132 of 200 ways..) 18.1 Kinetics deals with the rates of chemical reactions. In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the amount of reactant changing per unit time. Equilibrium refers to the condition where forward and reverse reactions are occurring at the same rates.

2. End Show © Copyright Pearson Prentice Hall > Rates of Reaction Slide 2 of 25 Collision Theory Rates of chemical reactions are often measured as a change in the number of moles during an interval of time. 18.1

3. End Show © Copyright Pearson Prentice Hall > Rates of Reaction Slide 3 of 25 Collision Theory Effective Collision 18.1 According to collision theory, atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy and have the proper orientation.

4. End Show © Copyright Pearson Prentice Hall > Rates of Reaction Slide 4 of 25 Collision Theory Ineffective Collision 18.1

5. The minimum energy that colliding particles must have in order to react is called the activation energy. 18.1 An activated complex is an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier. The activated complex is sometimes called the transition state.

6. Factors affecting Reaction Rates What four factors influence the rate of a chemical reaction? 18.1 The rate of a chemical reaction depends upon temperature, concentration, particle size, the use of a catalyst.

7. End Show Slide 7 of 25 © Copyright Pearson Prentice Hall > Rates of Reaction Factors Affecting Reaction Rates Temperature Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action. 18.1

8. End Show Slide 8 of 25 © Copyright Pearson Prentice Hall > Rates of Reaction Factors Affecting Reaction Rates Concentration 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. 18.1

9. End Show Slide 9 of 25 © Copyright Pearson Prentice Hall > Rates of Reaction Factors Affecting Reaction Rates Particle Size The minute size of the reactant particles (grain dust), and the mixture of the grain dust with oxygen in the air caused the reaction to be explosive, destroying the grain elevator. 18.1

10. End Show Slide 10 of 25 © Copyright Pearson Prentice Hall > Rates of Reaction Factors Affecting Reaction Rates Catalysts 18.1

11. A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium. The relative concentrations of the reactants and products at equilibrium constitute the equilibrium position of a reaction. At chemical equilibrium, no net change occurs in the actual concentration of the reactants and products – i.e. concentrations are constant. (Note this does not mean that the concentration of reactants and products are equal – avoid this common mistake).

12. Reversible Reactions How do the amounts of reactants and products change in a chemical system at equilibrium? At chemical equilibrium, no net change occurs in the actual amounts or concentration of the reactants and products. 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.

13. © Copyright Pearson Prentice Hall Slide 13 of 25 End Show Reversible Reactions At equilibrium, all three types of molecules are present. SO 2 and O 2 react to give SO 3 SO 3 decomposes to SO 2 and O 2

14. © Copyright Pearson Prentice Hall Slide 14 of 25 End Show Reversible Reactions

15. Three stresses can cause a change in the equilibrium position of a chemical system? changes in the concentration of reactants or products, changes in temperature, changes in pressure ( for equilibria involving gases ). 18.2 The French chemist Le Châtelier proposed what has come to be called 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.

16. © Copyright Pearson Prentice Hall Slide 16 of 25 End Show for Conceptual Problem 18.1

17. © Copyright Pearson Prentice Hall Slide 17 of 25 End Show Equilibrium Constants What does the value of the equilbrium constant, K eq, indicate about the equilibrium position of a reaction? The equilibrium constant (K eq ) is the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation. aA + bB cC + dD ←

18. © Copyright Pearson Prentice Hall Slide 18 of 25 End Show Equilibrium Constants A value of K eq greater than 1 means that products are favored over reactants; a value of K eq less than 1 means that reactants are favored over products.

19. © Copyright Pearson Prentice Hall Slide 19 of 25 End Show Kinetics and Equilibrium Types of Equilibria Physical Equilibria Phase Changes Saturated Solutions Chemical Equilibria Reversible Chemical Reactions

20. © Copyright Pearson Prentice Hall Slide 20 of 25 End Show Physical Equilibria – Phases Equilibria H 2 O (s)H 2 O (l) At 0 o C (273 K) there exists a phase equilibrium between solid and liquid H 2 O. At 100 o C (373 K) there exists a phase equilibrium between liquid and gaseous H 2 O. H 2 O (l) H 2 O (g)

22. © Copyright Pearson Prentice Hall Slide 22 of 25 End Show for Sample Problem 17.4 How many joules of heat are required to melt a 10.0 grams popsicle at 0 o C. Assume that the popsicle has the same heat of fusion as water.

23. © Copyright Pearson Prentice Hall Slide 23 of 25 End Show Heats of Vaporization and Condensation The quantity of heat absorbed by a melting a solid is exactly the same as the quantity of heat released when the liquid freezes; that is, ∆H fusion = –∆H solidification The quantity of heat absorbed by a vaporizing liquid is exactly the same as the quantity of heat released when the vapor condenses; that is, ∆H vaporization = –∆H condensation

24. © Copyright Pearson Prentice Hall Slide 24 of 25 End Show Heats of Vaporization and Condensation a.Enthalpy changes accompany changes in state. 17.3

25. © Copyright Pearson Prentice Hall Slide 25 of 25 End Show 17.3

26. © Copyright Pearson Prentice Hall Slide 26 of 25 End Show Heating (Endothermic) and Cooling (Exothermic) Curves Heating versus Cooling Curves

27. Physical Equilibria – Saturated Solutions Saturated solutions are another example involving physical equilibrium. The term “saturated solutions” refers to a solution containing the maximum amount of solute that will dissolve at a given temperature. The rate at which a substance crystallizes out of solution is equal to the rate at which it dissolves. pHET simulation for saturated solutions http://phet.colorado.edu/en/simulation/soluble-salts

28. Saturated Solution: = contains the maximum amount of solute for a given quantity of solvent at a constant temperature & pressure  if additional solute is added, it will not dissolve; rather it will precipitate out Unsaturated Solution: = a solution that contains less solute than a saturated solution at a given temperature & pressure  if additional solute is added, it will dissolve Supersaturated Solution: = contains more solute than it can theoretically hold at a given temperature  crystallization will be initiate if a very small “seed crystal” of solute is added **very unstable**

29. © Copyright Pearson Prentice Hall Slide 29 of 25 End Show Saturated Solution: = contains the maximum amount of solute for a given quantity of solvent at a constant temperature & pressure  if additional solute is added, it will not dissolve; rather it will precipitate out Unsaturated Solution: = a solution that contains less solute than a saturated solution at a given temperature & pressure  if additional solute is added, it will dissolve Supersaturated Solution: = contains more solute than it can theoretically hold at a given temperature  crystallization will be initiate if a very small “seed crystal” of solute is added **very unstable** Sample Individual Solubility Curve- Potassium nitrite http://www.stevespanglerscience.com/expe riment/00000078