1 / 63

Chapter 17: Chemical Equilibrium

CHEMISTRY Matter and Change. Chapter 17: Chemical Equilibrium. Table Of Contents. CHAPTER 17. Section 17.1 A State of Dynamic Balance Section 17.2 Factors Affecting Chemical Equilibrium Section 17.3 Using Equilibrium Constants. Click a hyperlink to view the corresponding slides. Exit.

chantellec
Download Presentation

Chapter 17: Chemical Equilibrium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHEMISTRY Matter and Change Chapter 17: Chemical Equilibrium

  2. Table Of Contents CHAPTER17 Section 17.1 A State of Dynamic Balance Section 17.2 Factors Affecting Chemical Equilibrium Section 17.3 Using Equilibrium Constants Click a hyperlink to view the corresponding slides. Exit

  3. A State of Dynamic Balance SECTION17.1 • List the characteristics of chemical equilibrium. • Write equilibrium expressions for systems that are at equilibrium. • Calculate equilibrium constants from concentration data. free energy: the energy that is available to do work—the difference between the change in enthalpy and the product of the entropy change and the absolute temperature

  4. A State of Dynamic Balance SECTION17.1 reversible reaction chemical equilibrium law of chemical equilibrium equilibrium constant homogeneous equilibrium heterogeneous equilibrium Chemical equilibrium is described by an equilibrium constant expression that relates the concentrations of reactants and products.

  5. A State of Dynamic Balance SECTION17.1 What is equilibrium? • Chemical reactions often reach a balancing point, or equilibrium. Forward: N2(g) + 3H2(g)  2NH3(g) Reverse: N2(g) + 3H2(g)  2NH3(g)

  6. A State of Dynamic Balance • A reversible reaction is a chemical reaction that can occur in both the forward and reverse directions, such as the formation of ammonia. N2(g) + 3H2(g) 2NH3(g) SECTION17.1 What is equilibrium?(cont.)

  7. A State of Dynamic Balance SECTION17.1 What is equilibrium?(cont.) • How does reversibility affect the production of ammonia? • Decreases in the concentrations of N2 and H2 cause the reaction to slow. • As soon as ammonia is present, the reverse reaction can occur, slowly at first, but at an increasing rate as the concentration of ammonia increases.

  8. A State of Dynamic Balance SECTION17.1 What is equilibrium?(cont.) • This continues until the two rates, the forward slowing and reverse increasing, are equal • At that point, the system has reached a state of equilibrium, figure d.

  9. A State of Dynamic Balance SECTION17.1 What is equilibrium?(cont.) • Chemical equilibrium is a state in which the forward and reverse reactions balance each other because they take place at equal rates. • Equilibrium is a state of action, not inaction.

  10. A State of Dynamic Balance SECTION17.1 Equilibrium Expressions • Some chemical systems have little tendency to react, others go to completion. • The majority reach a state of equilibrium with some of the reactants unconsumed.

  11. A State of Dynamic Balance SECTION17.1 Equilibrium Expressions(cont.) • Thelaw of chemical equilibriumstates that at a given temperature, a chemical system might reach a state in which a particular ratio of reactant and product concentrations has a constant value.

  12. A State of Dynamic Balance SECTION17.1 Equilibrium Expressions(cont.) • The value of Keq is constant only at a specified temperature. Keq > 1: Products are favored at equilibrium Keq < 1: Reactants are favored at equilibrium

  13. A State of Dynamic Balance SECTION17.1 Equilibrium Expressions(cont.) H2(g) +I2(g) 2HI(g) • This reaction is a homogeneous equilibrium, which means that all the reactants and products are in the same physical state.

  14. A State of Dynamic Balance SECTION17.1 Equilibrium Expressions(cont.) • When the reactants and products are present in more than one physical state, the equilibrium is called a heterogeneous equilibrium. • Ethanol in a closed flask is represented by C2H5OH(l) C2H5OH(g).

  15. A State of Dynamic Balance SECTION17.1 Equilibrium Constants • For a given reaction at a given temperature, Keq will always be the same regardless of the initial concentrations of reactants and products.

  16. Section Check SECTION17.1 A reaction is in equilibrium when: A.there are more products than reactants B.the amount of products equalsthe reactants C.the rate of the forward reaction is greater than the reverse reaction D.the rate of the forward and reverse reactions are equal

  17. Section Check SECTION17.1 The value of the equilibrium constant is constant for a given ____. A.temperature B.pressure C.volume D.density

  18. Factors Affecting Chemical Equilibrium SECTION17.2 • Describe how various factors affect chemical equilibrium. reaction rate: the change in concentration of a reactant or product per unit time, generally calculated and expressed in moles per liter per second. • Explain how Le Châtelier’s principle applies to equilibrium systems. Le Châtelier’s principle When changes are made to a system at equilibrium, the system shifts to a new equilibrium position.

  19. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle • Le Châtelier’s Principle was proposed in 1888 and states that if stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. • Stress is any kind of change in a system that upsets the equilibrium.

  20. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.) • Adjusting the concentrations of either the reactants or the products puts stress on a system in equilibrium. • Adding reactants increases the number of effective collisions between molecules and upsets the equilibrium.

  21. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.) • The equilibrium shifts to the right to produce more products. • The addition or removal of a reactant or product shifts the equilibrium in the direction that relieves the stress.

  22. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.) • Increasing pressure shifts the system to the right, and more products are formed. • Changing the volume (and pressure) of an equilibrium system shifts the equilibrium only if the number of moles of gaseous reactants is different from the moles of gaseous products.

  23. If the number of moles is the same on both sides of the balanced equation, changes in pressure and volume have no effect on the equilibrium. When the volume of the reaction vessel is decreased, the equilibrium position shifts towards whichever side has fewer total moles of gases. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.)

  24. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.) Lowering the piston decreases the volume and increases the pressure. As a result, more molecules of the products form. Their formation relieves the stress on the system. The reaction between CO and H2 is at equilibrium.

  25. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.) • Changes in temperature alter the equilibrium position and the equilibrium constant. • If heat is added to an equilibrium system, the equilibrium shifts in the direction in which the heat is used up.

  26. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle (cont.) • Any change in temperature results in a change in Keq.

  27. Factors Affecting Chemical Equilibrium SECTION17.2 Le Châtelier’s Principle(cont.) • A catalyzed reaction reaches equilibrium more quickly, but with no change in the amount of product formed.

  28. Section Check SECTION17.2 Which does NOT result in a shift of the equilibrium to the right? A.removing products B.adding reactants C.increasing concentration of reactants D.adding products

  29. Section Check SECTION17.2 Any change in ____ results in a change in Keq. A.temperature B.pressure C.volume D.concentration

  30. Using Equilibrium Constants SECTION17.3 • Determine equilibrium concentrations of reactants and products. solubility: the maximum amount of solute that will dissolve in a given amount of solvent at a specific temperature and pressure • Calculate the solubility of a compound from its solubility product constant. • Explain the common ion effect.

  31. Using Equilibrium Constants SECTION17.3 solubility product constant common ion common ion effect Equilibrium constant expressions can be used to calculate concentrations and solubilities.

  32. Using Equilibrium Constants or SECTION17.3 Calculating Equilibrium Concentrations • Equilibrium constants can be used to calculate unknown concentrations of products when other concentrations are known. • The equilibrium concentration for CH4 is 27.7mol/L

  33. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant • Some ionic compounds dissolve readily in water, and some barely dissolve at all. • The equilibrium constant expression for the dissolving of a sparingly soluble compound is called the solubility product constant, Ksp.

  34. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.) • The solubility product constant expression is the product of the concentrations of the dissolved ions, each raised to the power equal to the coefficient of the ion in the chemical equation.

  35. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.)

  36. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.) • The values in the table can be used to determine the solubility of a sparingly soluble compound. • Ksp can be used to predict whether a precipitate will form when any two ionic solutions are mixed. • Will a precipitate form in the above double-replacement reaction?

  37. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.) • In the above reaction, a precipitate is likely to form only if either product, KCl or Fe4(Fe(CN)6)3 has low solubility. • KCl has a Ksp= 21.7 • Fe4(Fe(CN)6)3 has a Ksp = 3.3 x 10-41 • So precipitate from KCl would be unlikely but for iron(III)ferrocyanide there is a possibility if the concentrations of its ions are large enough. • How large is large enough?

  38. First, you must calculate the concentrations of the ions. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.) • The table shows the concentration of the ions of reactants and products in the original solutions and in the mixture immediately after equal volumes of the two solutions were mixed.

  39. Now you can use thedata in the table to make a trial to see if the concentrations of Fe3+ and Fe(CN)64- in the mixed solution exceed the value of Ksp when substituted into the solubility product constant expression. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.)

  40. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.) • When you make the substitution, it will not necessarily give the solubility product constant. Instead, it provides a number called the ion product (Qsp). Qsp is a trial value that can be compared with Ksp.

  41. The outcome can have one of three outcomes: If Qsp < Ksp the solution is unsaturated and no precipitate will form. If Qsp = Ksp the solution is saturated and no change will occur. If Qsp > Ksp a precipitate will form, reducing the concentrations of the ions in the solution until the product of their concentrations in the Ksp expression equals the numerical value of Ksp. Using Equilibrium Constants SECTION17.3 The Solubility Product Constant(cont.) • Now you can compare Qsp and Ksp. – Qsp = 7.8 x 10-10 and Ksp = 3.3 x 10-41

  42. Using Equilibrium Constants SECTION17.3 The Common Ion Effect • Why is PbCrO4 less soluble in aqueous solution of K2CrO4 than in pure water? • The K2CrO4 solution contains CrO42– ions before any PbCrO4 dissolves.

  43. Using Equilibrium Constants SECTION17.3 The Common Ion Effect(cont.) • A common ion is an ion that is common to two or more ionic compounds. • The lowering of the solubility of a substance because of the presence of a common ion is called the common ion effect.

  44. Section Check SECTION17.3 The presence of a common ion ____ the solubility of the dissolved substance. A.decreases B.increases C.does not change D.speeds up

  45. Section Check SECTION17.3 If Qsp > Ksp ____. A.the solution is unsaturated and no precipitate will form B.the solution is saturated and no precipitate will form C.a precipitate will form, reducing the concentrations of the ions in the solution D.a common ion must be present

  46. Chemical Equilibrium CHAPTER17 Resources Chemistry Online Study Guide Chapter Assessment Standardized Test Practice

  47. A State of Dynamic Balance SECTION17.1 Study Guide Key Concepts • A reaction is at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction. • The equilibrium constant expression is a ratio of the molar concentrations of the products to the molar concentrations of the reactants with each concentration raised to a power equal to its coefficient in the balanced chemical equation. • The value of the equilibrium constant expression, Keq, is constant for a given temperature.

More Related