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Chemistry 18.2

Chemistry 18.2. Reversible Reactions and Equilibrium. 18.2.

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Chemistry 18.2

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  1. Chemistry 18.2

  2. Reversible Reactions and Equilibrium 18.2 • 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.

  3. 18.2 Reversible Reactions • Reversible Reactions • How do the amounts of reactants and products change in a chemical system at equilibrium?

  4. 18.2 Reversible Reactions • At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.

  5. 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.

  6. 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.

  7. 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.

  8. 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. • A + B 25% C + D • Means that at equilibrium, only 25% of the reactants A & B have been converted to products C &D.

  9. 18.2 Reversible Reactions

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

  11. 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?

  12. 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.

  13. 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.

  14. Factors Affecting Equilibrium: Le Châtelier’s Principle • Simulation 24 • Simulate Le Châtelier’s principle for the synthesis of ammonia.

  15. 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.

  16. An increase in concentration of a particular entity will result in a shift to the opposite side of the equation. • This is because an increase in concentration means a better chance of a reaction taking place • A + B shifts right (more products) C + D

  17. A decrease in concentration of a particular entity will result in a shift to the same side of the equation. • This is because an decrease in concentration means less chance of a reaction taking place • A + Bshifts left (more reactants) C + D

  18. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • 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. An increase in temperature results in a shift to the opposite side of the equation as the “heat”. • This is because an increase in temperature means more collisions and a better chance of a reaction taking place • A + B + HEATshifts right (more products) C + D

  20. A decrease in temperature will result in a shift to the same side of the equation as the “heat”. • This is because a decrease in temperature means less collisions and less chance of a reaction taking place • A + B + HEATshifts left (more reactants)C + D

  21. 18.2 Factors Affecting Equilibrium: Le Châtelier’s Principle • Pressure • Pressure affects a mixture of nitrogen, hydrogen, and ammonia at equilibrium

  22. An increasein pressure (i.e. a decrease in volume) results in a shift to the side of the equation with less moles of gas entities. • This is because an increase in pressure forces the smaller gas entities to come together to be more efficient in space (bigger molecules but less of them). • 2 A(g) + B(g)shifts right (more products) A2B (g) • (3 moles of gas) (1 mole of gas)

  23. A decreasein pressure (i.e. an increase in volume) results in a shift to the side of the equation with more moles of gas entities. • This is because an decrease in pressure forces the larger gas entities to break up to fill the void in space (smaller molecules but more of them). • 2 A(g) + B(g)shifts left (more reactants) A2B (g) • (3 moles of gas) (1 mole of gas)

  24. Conceptual Problem 18.1

  25. Conceptual Problem 18.1

  26. Conceptual Problem 18.1

  27. for Conceptual Problem 18.1 Problem Solving 18.6 Solve a similar problem with the help of an interactive guided tutorial.

  28. 18.2 Equilibrium Constants • Equilibrium Constants • What does the value of Keq indicate about the equilibrium position of a reaction?

  29. 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.

  30. 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.

  31. 18.1

  32. 18.1

  33. 18.1

  34. 18.1

  35. for Sample Problem 18.1 Problem Solving 18.7 Solve Problem 7 with the help of an interactive guided tutorial.

  36. 18.2

  37. 18.2

  38. 18.2

  39. 18.2

  40. for Sample Problem 18.2 Problem Solving 18.9 Solve Problem 9 with the help of an interactive guided tutorial.

  41. 18.2 Section Quiz. • 18.2.

  42. 18.2 Section Quiz. • 1. In a reaction at equilibrium, reactants and products • decrease in concentration. • form at equal rates. • have equal concentrations. • have stopped reacting.

  43. 18.2 Section Quiz. • 2. In the reaction 2NO2(g)  2NO(g) + O2(g), increasing the pressure on the reaction would cause • the amount of NO to increase. • the amount of NO2 to increase. • nothing to happen. • the amount of O2 to increase.

  44. 18.2 Section Quiz. • 3. Changing which of the following would NOT affect the equilibrium position of a chemical reaction? • concentration of a reactant only • concentration of a product only • temperature only • volume only

  45. 18.2 Section Quiz. • 4. For the following reaction, Keq = 1. • A(g) + B(g)  C(g) + D(g) Therefore, at equilibrium • [C] = [A]. • [A][B] = 0. • [AB] = [CD] = 1. • [A][B] = [C][D].

  46. END OF SHOW

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