Reaction Rates and Equilibrium

1. Reaction Rates and Equilibrium Chapter 18

2. 18.1 Rates of Reaction • The heat given off by the corrosion reaction of an iron-magnesium alloy with salt water can produce a hot meal. The rate of reaction is increased by adding salt water, so heat is produced rapidly. You will learn some ways in which the rate of a reaction can be increased.

3. 18.1 Collision Theory • Collision Theory • How is the rate of a chemical change expressed?

4. 18.1 Collision Theory • In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the amount of reactant changing per unit time.

5. 18.1 Collision Theory • A rate is a measure of the speed of any change that occurs within an interval of time.

6. 18.1 Collision Theory • Rates of chemical reactions are often measured as a change in the number of moles during an interval of time.

7. 18.1 Collision Theory • 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.

8. 18.1 Collision Theory • Effective Collision

9. 18.1 Collision Theory • Ineffective Collision

10. 18.1 Collision Theory • The minimum energy that colliding particles must have in order to react is called the activation energy.

11. 18.1 Collision Theory • An activated complex is an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier.

12. 18.1 Factors Affecting Reaction Rates • Factors Affecting Reaction Rates • What four factors influence the rate of a chemical reaction?

13. 18.1 Factors Affecting Reaction Rates • The rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst.

14. Factors Affecting Reaction Rates • Animation 22 • Explore several factors that control the speed of a reaction.

15. 18.1 Factors Affecting Reaction Rates • Temperature • Storing foods in a refrigerator keeps them fresh longer. Low temperatures slow microbial action.

16. 18.1 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.

17. 18.1 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. 18.1 Factors Affecting Reaction Rates • Catalysts

19. 18.2 Reversible Reactions and Equilibrium • In the early 1900s, German chemists refined the process of making ammonia from elemental nitrogen and hydrogen.This process allows the manufacture of nitrogen fertilizers. You will learn how reaction conditions can influence the yield of a chemical reaction.

20. 18.2 Reversible Reactions • Reversible Reactions • How do the amounts of reactants and products change in a chemical system at equilibrium?

21. 18.2 Reversible Reactions • At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.

22. 18.2 Reversible Reactions • 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.

23. 18.2 Reversible Reactions • A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

24. 18.2 Reversible Reactions SO3 decomposes to SO2 and O2 SO2 and O2 react to give SO3 At equilibrium, all three types of molecules are present.

25. Reversible Reactions • Animation 23 • Take a close look at a generalized reversible reaction.

26. 18.2 Reversible Reactions • 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.

27. 18.2 Reversible Reactions

28. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Factors Affecting Equilibrium: Le Châtelier’s Principle • What three stresses can cause a change in the equilibrium position of a chemical system?

29. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Stresses that upset the equilibrium of a chemical system include changes in the concentration of reactants or products, changes in temperature, and changes in pressure.

30. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • 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.

31. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Concentration • Rapid breathing during and after vigorous exercise helps reestablish the body’s correct CO2:H2CO3 equilibrium, keeping the acid concentration in the blood within a safe range.

32. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Temperature • Dinitrogentetroxide 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. • 2NO2(g) ⇆ N2O4(g) + heat

33. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Pressure • Pressure affects a mixture of nitrogen, hydrogen, and ammonia at equilibrium • N2(g) + 3H2(g) ⇆ 2NH3(g)

34. Conceptual Problem 18.1

35. for Conceptual Problem 18.1

36. 18.2 Equilibrium Constants • Equilibrium Constants • What does the value of Keq indicate about the equilibrium position of a reaction?

37. 18.2 Equilibrium Constants • The equilibrium constant (Keq) 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.

38. 18.2 Equilibrium Constants • A value of Keq greater than 1 means that products are favored over reactants; a value of Keq less than 1 means that reactants are favored over products.

39. 18.1

40. for Sample Problem 18.1

41. 18.2

42. for Sample Problem 18.2

43. 18.3 Solubility Equilibrium • Barium sulfate is ingested by a patient before X-ray images of the digestive tract are taken. Barium sulfate absorbs the X-rays, thereby producing light areas on the developed X-ray film. However, barium salts are usually toxic. You will learn why patients can ingest this poisonous substance without harm.

44. 18.3 The Solubility Product Constant • The Solubility Product Constant • What is the relationship between the solubility product constant and the solubility of a compound?

45. 18.3 The Solubility Product Constant • The solubility product constant (Ksp), equals the product of the concentrations of the ions, each raised to a power equal to the coefficient of the ion in the dissociation equation. • The smaller the numerical value of the solubility product constant, the lower the solubility of the compound.

46. 18.3 The Solubility Product Constant

47. 18.3 The Solubility Product Constant

48. 18.3 The Solubility Product Constant • Silver chloride is slightly soluble in water.

49. 18.3 The Solubility Product Constant • Scale, formed by the precipitation of slightly soluble salts, builds up around faucets.

50. 18.3