Study Guide for Module 13 An Introduction to Equilibrium

Transcription

1 Chemistry 1020, Module 13 Name Study Guide for Module 13 An Introduction to Equilibrium Reading Assignment: Section 12.1 and Chapter 13 of Chemistry, 6th Edition by Zumdahl. Guide for Your Lecturer: 1. An Overview Of Kinetics 2. An Overview of Equilibrium 3. Calculating Equilibrium Constants from Equilibrium Concentrations or Pressures 4. Equilibrium From A Slightly Different Viewpoint 5. Predicting the Direction in Which a Reaction Will Proceed 6. Stoichiometric Changes as a System Goes Toward Equilibrium 7. Factors Which Affect Equilibrium 8. Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied #1 9. Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #2 10. Altering or Combining Equilibrium Reactions Homework Note: indicates problems to be stressed on drill quizzes and hour exams. An Overview Of Kinetics 1a) Define kinetics. (p. 556) b) Distinguish between the symbols [X] and (X). (We will use [X] to indicate the concentration of X in moles/liter at equilibrium and (X) to indicate concentration, also in moles/liter, when not at equilibrium.) c) What does a chemist mean by rate of a reaction? (p. 557) d) On the axes below draw two sketches, one showing how concentration of a reactant changes with time and the other showing how the concentration of a product changes with time as a chemical reaction proceeds. (p. 562) (reactant) (product) time--> time--> Xavier University of Louisiana 83

2 Chemistry 1020, Module 13 An Overview of Equilibrium 2a) What does at equilibrium mean in the ordinary world? b) What two conditions must exist for a chemical system to be described as being at equilibrium. (1-There is no change in concentration of reactants or products with time. 2-Lack of change does not mean no reaction is occurring but rather that forward and reverse rates are equal. p ) - - c) Would chemical equilibrium as described in b above best be considered to be static or dynamic? Explain. d) Distinguish between heterogeneous and homogeneous equilibria. (An equilibrium is said to be homogeneous if all species are in a single homogeneous phase. Otherwise it is heterogeneous.) e) Define partial pressure. (p ) f) List the elements which appear as diatomic species under normal conditions. (From Chem1010, Module 1) List the elements which are gaseous under normal conditions. (From Chem1010, Module 1) List the elements which are liquid under normal conditions. (From Chem1010, Module 1) g) State the Law of Mass Action in terms of concentrations and in terms of partial pressures for a reaction in which A reacts with B to form C and D. (All are gases.) The balancing coefficients in the equation are w, x, y, and z, respectively. (p. 613) Balanced equation: Equation in terms of concentrations: Equation in terms of pressures: h) What is the name of... One of the equations in g? The constant in g? i) Which reactants and products appear in an equilibrium expression? 84 Xavier University of Louisiana

3 Chemistry 1020, Module 13 Name An Overview of Equilibrium (continued) 2j) What does a double arrow (or ) between reactants and products mean in a chemical equation? (That the reaction is reversible and will reach equilibrium.) k) Write the balanced chemical equation for the reaction indicated. Then write the equilibrium expression in terms of concentrations (and pressures if applicable). (pp ) S1. Chlorine reacts with fluorine to produce ClF(g). Balanced chemical equation Cl2(g) + F2(g) 2 ClF(g) Equilibrium expression in terms of concentrations Kc = [ClF] 2 [Cl2][F2] Equilibrium expression in terms of partial pressures (if applicable) Kp = (P ClF) 2 Note: The partial pressure PCl2PF2 of ClF is squared S2. Aqueous ammonia reacts with water to produce ammoniumhydroxide. Balanced chemical equation NH3(aq) + H2O(l) NH4OH(aq) Equilibrium expression in terms of concentrations Kc = [NH 4OH] [NH3] Equilibrium expression in terms of partial pressures (if applicable) Note: There is no K P expression because there are no gases A. Carbon dioxide(g) decomposes to produce carbon monoxide(g) and oxygen(g). Balanced chemical equation Equilibrium expression in terms of concentrations Equilibrium expression in terms of partial pressures (if applicable) B. Calcium carbonate decomposes in a closed container into carbon dioxide (a gas) and calcium oxide. Balanced chemical equation Equilibrium expression in terms of concentrations Equilibrium expression in terms of partial pressures (if applicable) Xavier University of Louisiana 85

4 Chemistry 1020, Module 13 An Overview of Equilibrium (continued) 2k) Write the balanced chemical equation for the reaction indicated. Then write the equilibrium expression in terms of concentrations (and pressures if applicable). (pp ) C. Hydrogen reacts with chlorine to produce hydrogen chloride. HCl is a gas. Balanced chemical equation Equilibrium expression in terms of concentrations Equilibrium expression in terms of partial pressures (if applicable) D. Aqueous sulfur dioxide reacts with water to form sulfurous acid. Balanced chemical equation Equilibrium expression in terms of concentrations Equilibrium expression in terms of partial pressures (if applicable) E. Aqueous silver(i) ions react with aqueous chloride ions to produce silver(i) chloride. Equilibrium expression in terms of concentrations Equilibrium expression in terms of partial pressures (if applicable) F. Carbonic acid (H2CO3, i.e. CO2 in H2O) decomposes to produce water and aqueous carbon dioxide. Balanced chemical equation Equilibrium expression in terms of concentrations Equilibrium expression in terms of partial pressures (if applicable) l) How are Kc and Kp related for a chemical system? (p. 620) 86 Xavier University of Louisiana

5 Chemistry 1020, Module 13 Name Calculating Equilibrium Constants from Equilibrium Concentrations or Pressures Note: In working equilibrium problems (something we will do many times in this and following modules, ALWAYS do the following in the order indicated... ❶Write the balanced chemical equation in equilibrium. ❷Write the equilibrium expression. ❸Calculate concentrations (or pressures) of substances which appear in the equilibrium expression. ❹Substitute the concentrations from 3 into the equilibrium expression. ➎Do whatever is necessary to complete the problem. 3. S. At a high temperature, hydrogen reacts with iodine vapor to produce hydrogen iodide (g). What is the equilibrium constant (Kc) if there are 0.20 moles of hydrogen, 0.30 moles of iodine, and 1.2 moles of hydrogen iodide when the system reaches equilibrium in a 2.0 liter container? (pp ) ❶ H2(g) + I2(g) 2 HI(g) [I2] = 0.30 mol I L = M I2 ❷ Kc = [HI] 2 ❹ Now substitute [ ] s into equilibrium expression [H2][I2] 1.2 mol HI ❸ [HI] = 2.0 L [H2] = 0.20 mol H L = M HI Kc = = M H2 ➎ Kc = 24 (0.600) 2 (0.100)(0.150) = A. Nitrogen reacts with hydrogen to form ammonia, a gas. If at equilibrium a 5.2 liter container is found to contain 2.0 moles of nitrogen, 0.33 moles of ammonia, and 0.45 moles of hydrogen, what is the equilibrium constant (Kc) for the reaction? B. For the reaction 3 A(g) + B(g) 2 C (g), an equilibrium mixture in a 2.0 liter container is found to have the following partial pressures: 2.0 atm A, 0.25 atm B, and 0.50 atm C. Calculate the value of the equilibrium constant (Kp) for the reaction. Xavier University of Louisiana 87

6 Chemistry 1020, Module 13 Calculating Equilibrium Constants from Equilibrium Concentrations (continued) 3. C. Hydrogen reacts with oxygen to form water vapor. What is the equilibrium constant (Kc) if there are 0.12 moles of oxygen, 0.51 moles hydrogen, and 2.0 moles of water in a 12 liter container when the system reaches equilibrium? D. For the reaction 2 A(g) B(g) + C(g) an equilibrium mixture in a 5.2 liter container is found have the following partial pressures: 1.0 atm A, 2.0 atm B, and 0.50 atm of C. Calculate the value of the equilibrium constant (Kp) for this reaction. E. If the equation PCl5(g) PCl3(g) + Cl2(g) is in equilibrium in a 2.3 liter container at a certain temperature, it is found that there are moles of PCl3, moles of Cl2, and 1.9 moles of PCl5 in the container. What is the equilibrium constant (Kc) for the reaction at this temperature? F. If the equation 2 A(g) + B(g) 2 C(g) is in equilibrium in a 3.0 liter container at a certain temperature, it is found that the partial pressures of A, B, and C are: 1.7 atm A, 1.2 atm B, and 0.92 atm C in the container. What is the equilibrium constant (Kp) for the reaction at this temperature? (pp ) 88 Xavier University of Louisiana

7 Chemistry 1020, Module 13 Name Equilibrium From A Slightly Different Viewpoint 4a) Given systems with the following values of equilibrium constants, predict the relative amounts of products and reactants at equilibrium. Value of equilibrium Relative amounts of Value of equilibrium Relative amounts of constant reactants and products constant reactants and products S. 4.6*10 5 K>>1 so 1.3*10-8 K<<1 so more products than more reactants than K>>1 reactants at K<<1 products at equilibrium equilibrium A. 8.5* *10-9 B *10 3 C. 9.6* *10 7 D. 4.2* *10-10 E. 8.6* *10-9 F. 9.1* *10 7 b) What is the relationship between the equilibrium constant and the rate at which a chemical reaction occurs? (There is NO relationship between the two.) c) Chemists often use the terms shift to the right and shift to the left in describing changes in a chemical system. Provide the indicated information about each. ("Shift to the right" means that all products increase and all reactants decrease. "Shift to the left" means that all products decrease and all reactants increase.) Change of system Shift to the right What happens to reactants and products as change occurs Initial/Change/Final Chart for the reaction 2A + 1B 2C + 1D illustrating change by placing signs ( + or - ) in the Change Shift to the left d) What is ALWAYS the relationship between the signs on changes in reactants and products when a shift occurs? (ALL reactants have one sign and ALL products have the opposite.) Xavier University of Louisiana 89

8 Chemistry 1020, Module 13 Equilibrium From A Slightly Different Viewpoint (continued) 4e) If the following diagrams represent views of a system at equilibrium at the molecular level, indicate the relative magnitude of the equilibrium constants for each system. Then draw a similar diagram that correctly represents the system at the molecular level after the indicated shift. Reaction and representation Draw an INITIAL/CHANGE/FINAL chart at equilibrium showing the system shifting as indicated S. Rxn: 2A + 2B 1C + 2D Equilibrium Shift: To the left Products decrease Composition Reactants increase A - 8 Molecular level view: B - 9 C - 2 2A + 2B 1C + 2D A B C A D - 3 initial B B A final B D Relative size of K C D A Final composition: B A More reactants A = 10, B = 11, C = 1, D = 1 B B than products A B D so K<1 Note: This is only 1 of the possible B A A answers. A. Rxn: 1A + 2B 2C + 2D Equilibrium Shift: To the right Composition Molecular level view: C C C D C B C B D Relative size of K C D A C D B D A C D C D D B. Rxn: 2A + 2 B 1C + 2D Equilibrium Shift: To the left Composition Molecular level view: C C C D C B C D D Relative size of K C D A C D D D B B D C D C 90 Xavier University of Louisiana

9 Chemistry 1020, Module 13 Name Equilibrium From A Slightly Different Viewpoint (continued) 4e) If the following diagrams represent views of a system at equilibrium at the molecular level, indicate the relative magnitude of the equilibrium constants for each system. Then draw a similar diagram that correctly represents the system at the molecular level after the indicated shift. Reaction and representation Draw an INITIAL/CHANGE/FINAL chart at equilibrium showing the system shifting as indicated C. Rxn: Equilibrium Shift: To the right Composition Molecular level view: Relative size of K D. Rxn: Equilibrium Shift: To the left Composition Molecular level view: Relative size of K E. Rxn: 3A + 2B 1C + 2D Equilibrium Shift: To the right Composition Molecular level view: A A C D C B C B B Relative size of K C D A A D B D C D D F. Rxn: 1A + 2B 3C + 2D Equilibrium Shift: To the left Composition Molecular level view: C C C D C B C D D Relative size of K C D A D D B B D C D C Xavier University of Louisiana 91

10 Chemistry 1020, Module 13 Predicting the Direction in Which a Reaction Will Proceed 5. In many instances, chemists begin an experiment with a container which contains reactants but not products. In this type of experiment, we know the reaction proceeds so as to decrease reactants and increase products. In other instances, however, chemists begin an experiment with a container which contains both reactants and products and must determine the direction in which the reaction will occur to reach equilibrium. I.E. Must determine whether some reactants will combine to form products or whether products will combine (decompose) to form reactants. The procedure for making such a determination is: ❶Write the balanced chemical equation, ❷Write the equilibrium expression. ❸Set up a concentration quotient (Q) which looks like the equilibrium expression EXCEPT that it contains nonequilibrium (i.e. initial or given) rather than equilibrium concentrations. ❹Calculate nonequilibrium concentrations of all species in the concentration quotient expression. ➎Substitute nonequilibrium concentrations into the concentration quotient expression and calculate. ❻Compare the value of the concentration quotient with that of K to see how Q must change to become K as equilibrium is reached. If K>Q, reaction will proceed to the right (i.e. some reactants will combine to form products). If K<Q, reaction will proceed to the left (i.e. some products will decompose to form reactants). S. Given: 2 NO2(g) N2O4(g); K = 4.73 at 25 o C, a) In which way does the system shift to reach equilibrium if 8.0 moles N2O4 and 1.5 moles of NO2 are placed in a 2.0 liter container? SHOW ALL WORK. (pp ) ❶2 NO2(g) N2O4(g) ❷Kc = [N 2O4] [NO2] 2 = 4.73 (NO 2) = 1.5 mol NO L = M NO2 ❸Q = (N 2O4) (NO2) 2 ➎Q = 4.00 (0.750) 2 = 7.1 ❹(N2O4) = 8.0 mol N 2O4 2.0 L = 4.00 M N2O4 ❻Q > K, Therefore, reaction shifts to left. b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? (NO2) increases, (N2O4) decreases A. Given: 2 CO2(g) 2 CO(g) + O2(g); K = 6.8*10 2 at 2500K, a) In which way does the system shift to reach equilibrium if 2.3 moles of carbon monoxide, 2.9 moles of oxygen, and 4.6 moles of carbon dioxide are placed in a 12 liter container? b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? 92 Xavier University of Louisiana

11 Chemistry 1020, Module 13 Name Predicting the Direction in Which a Reaction Will Proceed (continued) 5. B. Given: 2 NO2(g) 2 NO (g) + O2 (g); K = 6.8*10-2 at 190 o C, a) In which way does the system shift to reach equilibrium if 3.0 moles of each of the substances is placed in a 5.8 liter container? b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? C. Given: H2(g) + I2(g) 2 HI(g); K = 50.0 at 448 o C, a) In which way does the system shift to reach equilibrium if 2.0 moles of hydrogen, 8.1 moles of iodine, and 14 moles of hydrogen iodide are placed in a 22 liter container and allowed to come to equilibrium? b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? D. Given: 2 SO2(g) + O2(g) 2 SO3(g); K = 6.5 at 900K, a) In which direction does the reaction shift to reach equilibrium if 5.3 moles of sulfur dioxide, 2.9 moles of oxygen, and 13 moles of sulfur trioxide are placed in a 11 liter container and allowed to go to equilibrium? b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? Xavier University of Louisiana 93

12 Chemistry 1020, Module 13 Predicting the Direction in Which a Reaction Will Proceed (continued) 5. E. Given: 2 NO2(g) 2 NO(g) + O2(g); K = 1.2*10-5 at 200 o C, a) In which direction does the system shift to reach equilibrium if 3.0 moles of NO2, 3.5 moles of NO, and 4.0 moles of O2 are placed in a 18 liter container? b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? F. Given: CO(g) + H2O(g) CO2(g) + H2(g); K = 0.64 at 800 o C, a) In which direction does the system shift to reach equilibrium if 8.0 moles of carbon monoxide, 4.0 moles of water, 11 moles of carbon dioxide, and 3.0 moles of hydrogen are placed in a 25 liter container? b) What happens to the amounts of each of the reactants and products as it proceeds toward equilibrium? 94 Xavier University of Louisiana

13 Chemistry 1020, Module 13 Name Stoichiometric Changes as a System Goes Toward Equilibrium 6. S1. For the reaction, N2O4(g) 2 NO2(g), how much N2O4 is present at equilibrium if the initial amounts of N2O4 and NO2 are 3.0 moles and 1.0 moles, respectively, and the amount of NO2 at equilibrium is 1.3 moles. Use an INITIAL/CHANGE/FINAL chart to organize your work. mol N2O4 used = 0.30 mol NO2 * (1 mol N 2O4) (2 mol NO2) = N2O4 2 NO2 = 0.15 mol N2O4 used initial R final Therefore, 2.85 = 2.9 moles N2O4 remain at equilibrium. S2. For the reaction, 2 SO3(g) O2(g) + 2 SO2(g), how much SO3 is present at equilibrium if the initial amounts of SO3, SO2, and O2 are 4.0 moles, 3.0 moles, and 2.5 moles, respectively, and the amount of O2 at equilibrium is 1.7 moles? Use an INITIAL/CHANGE/FINAL chart to organize your work. mol SO3= 0.80 mol O2 * (2 mol SO 3) (1 mol O2) = 2SO3 O2 + 2 SO2 = 1.6 mol SO3 produced initial final mol SO3 = = 5.6 mol SO3 at equilibrium final A. How much O2 remains in a system in which 2 H2 (g) + 1 O2(g) 2 H2O(g) is in equilibrium if the initial amount of hydrogen is 1.0 mole, of oxygen is 1.0 mole, and of water is 0 mole and there is 0.50 moles of water at equilibrium? B. How much O2 remains in a system in which 2 H2 (g) + 1 O2(g) 2 H2O(g) is in equilibrium if the initial amount of H2, O2, and H2O were 6.2 moles, 8.1 moles, and 4.2 moles, respectively, and there are 7.2 moles of H2 at equilibrium? C. 3.0 moles of hydrogen, 1.0 mole of nitrogen, and 1.0 mole of ammonia are placed in a container and allowed to come to equilibrium according to the equation, 1 N2 + 3 H2 2 NH3. If there are 1.5 moles of ammonia at equilibrium, how much hydrogen is present at equilibrium? All of the substances are gases. Xavier University of Louisiana 95

14 Chemistry 1020, Module 13 Stoichiometric Changes as a System Goes Toward Equilibrium (continued) 6. D. For the reaction 1 N2 + 3 H2 2 NH3, how much nitrogen remains at equilibrium if the system contains 4.9, 8.2, and 9.1 moles of hydrogen, nitrogen, and ammonia, respectively, at the beginning and is found to contain 10.5 moles of ammonia at equilibrium? E moles of nitrogen, 1.00 mole of oxygen, and 3.00 moles of dinitrogen oxide are placed in a container and allowed to come to equilibrium according to the equation, 2 N2 + 1 O2 2 N2O. If there are 1.25 moles of dinitrogen oxide at equilibrium, how much nitrogen is present at equilibrium? All of the substances are gases. F moles of nitrogen, 3.00 moles of oxygen, and 1.00 mole of nitrogen oxide are placed in a container and allowed to come to equilibrium according to the equation, 1 N2 + 1 O2 2 NO. If there are 0.25 moles of nitrogen oxide at equilibrium, how much nitrogen is present at equilibrium? All of the substances are gases. 96 Xavier University of Louisiana

15 Chemistry 1020, Module 13 Name Factors Which Affect Equilibrium 7a) State LeChatelier's Principle. (p ) b) List four factors which affect the position of equilibrium and indicate the effect of each by completing the following table. (1. Concentration of reactants or products: Adding a reactant causes the reaction to shift to the right thereby decreasing other reactants and increasing products. Removing a reactant causes the reaction to shift to the left thereby increasing other reactants and decreasing products. Adding or removing a product causes the reverse effect. 2. Temperature: The way in which position of equilibrium is related to temperature depends on whether the reaction is endothermic or exothermic. If it is endothermic, increasing the temperature (adding heat) causes the reaction to shift to the right. If it is exothermic, increasing the temperature causes it to shift to the left. 3. Pressure (gases only): If pressure is increased, the system will shift toward the side with the smaller number of moles of gas. 4. Volume of the container (gases only): If volume is increased, the system will shift toward the side with the larger number of moles of gas. One way to remember this is that P and V for a gas are inversely proportional so if V increases, P decreases. Also see pages in the text.) Factor (Stress) How a change in the factor changes a system at equilibrium 1) 2) 3) 4) c) Which of the factors above affects the value of the equilibrium constant? (p. 646) d) What is the effect of adding a catalyst to a reversible reaction at equilibrium? (A catalyst speeds up both the forward and the reverse reaction. Therefore, a system which is at equilibrium shows no overall change when a catalyst is added.) e) Restate LeChatelier s Principle in terms of the change which caused a stress on a system. (The shift is ALWAYS opposite to the stress. Thus, if you stress a system at equilibrium by adding substance A which is in the homogeneous phase, the system will shift so as to decrease the amount of A present after the stress.) f) In the chart below summarize the changes in products and reactants for the indicated shift using arrows enclosed in parentheses. I.E. Instead of using signs to show changes as in 4c, use arrows in parentheses to show increases (arrows point upward) and decreases (arrows point down). Direction Effect on Reactants Effect on Products of Shift left right Xavier University of Louisiana 97

16 Chemistry 1020, Module 13 Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #1 8. S. a) Write the balanced chemical equation, including heat, for the endothermic reaction of hydrogen with oxygen to produce H2O2 (gas). heat + H2(g) + O2(g) H2O2 (g) b) Write the equilibrium expression for the reaction in a above.(p ) K = [H 2O2] [H2][O2] c) Copy the balanced chemical equation above (including heat change), into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium. Note: Do by a) putting a large arrow in the chart to show the stress and then b) putting the direction of shift and smaller arrows in parentheses to show the shift. (pp ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift H2(g) O2(g) Heat H2O2(g) 1-add ( ) ( ) ( ) ( ) None hydrogen 2-remove <- ( ) ( ) ( ) ( ) None oxygen 3-increase T ( ) ( ) ( ) ( ) Increase 4-add a catalyst 5-add hydrogen peroxide 6-decrease V container* None No Effect No Effect No Effect No Effect No Effect <- ( ) ( ) ( ) ( ) None ( ) ( ) ( ) ( ) None *Since V does not appear in the equation, you cannot show the stress in the chart. The reasoning to obtain the answer is: V so P (P and V are inversely proportional for gases). For P system should shift to decrease pressure ( ). This means it shifts to the right since there is only 1 molecule of gas on the products side of the equation and there are 2 molecules of gas on the reactants side. Show symbolically by V, so P which causes shift ( ). A. a) Write the balanced chemical equation, including heat, for the reaction of sulfur dioxide(g) with oxygen to produce sulfur trioxide(g). The reaction is exothermic b) Write the equilibrium expression for the reaction in a above.( ) c) Copy the balanced chemical equation from a above, including heat change, into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium in the same manner demonstrated in lecture.( ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift 1-add oxygen 2-remove SO3 3-decrease T 4-add a catalyst 5-add sulfur dioxide 6-decrease container V 98 Xavier University of Louisiana

17 Chemistry 1020, Module 13 Name Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #1 (continued) 8. B. a) Write the balanced chemical equation, including heat, for the reaction of nitrogen with oxygen to produce dinitrogen oxide (g). The reaction is endothermic b) Write the equilibrium expression for the reaction in a above. ( ) c) Copy the balanced chemical equation from a above, including heat change, into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium in the same manner demonstrated in lecture. (pp ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift 1-remove oxygen 2-remove N2O 3-increase T 4-add a catalyst 5-add nitrogen 6-increase container V C. a) Write the balanced chemical equation, including heat, for the reaction of hydrogen with oxygen to produce water (g). The enthalpy change for the reaction is kj b) Write the equilibrium expression for the reaction in a above. (p ) c) Copy the balanced chemical equation from a above, including heat change, into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium in the same manner demonstrated in lecture. (pp ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift 1-remove hydrogen 2-add oxygen 3-decrease T 4-add a catalyst 5-add water 6-increase container V Xavier University of Louisiana 99

18 Chemistry 1020, Module 13 Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #1 (continued) 8. D. a) Write the balanced chemical equation, including heat, for the reaction of hydrogen with chlorine to produce hydrogen chloride (g). The enthalpy change is kj b) Write the equilibrium expression for the reaction in a above. (p ) c) Copy the balanced chemical equation from a above, including heat change, into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium in the same manner demonstrated in lecture. ( ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift 1-remove hydrogen 2-add chlorine 3-decrease T 4-add a catalyst 5-add HCl 6-increase pressure E. a) Write the balanced chemical equation, including heat, for the reaction of phosphorous with chlorine to produce PCl5 (g). The enthalpy change for the reaction is kj. FYI: Phosphorus occurs as P4(s) b) Write the equilibrium expression for the reaction in a above. (p ) c) Copy the balanced chemical equation from a above, including heat change, into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium in the same manner demonstrated in lecture. (pp ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift 1-remove PCl5 2-add phosphorus 3-decrease T 4-add a catalyst 5-add chlorine 6-decrease container V 100 Xavier University of Louisiana

19 Chemistry 1020, Module 13 Name Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #1 (continued) 8. F. a) Write the balanced chemical equation, including heat, for the reaction of nitrogen with iodine to produce nitrogen triodide gas at a temperature where iodine is a gas. The enthalpy change for the reaction is exothermic b) Write the equilibrium expression for the reaction in a above. (p ) c) Copy the balanced chemical equation from a above, including heat change, into the heading of the table below. Then use LeChatelier's Principle to fill in the table indicating the effect of each of the indicated stresses on the reaction if at equilibrium in the same manner demonstrated in lecture. (pp ) Change Direction Overall Effect on Reactants Overall Effect on Products Effect on K of Shift 1-add nitrogen 2-remove NI3 3-increase T 4-add a catalyst 5-add iodine 6-decrease container V Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #2 9. S. Use the equation in the corresponding problem in #8S to answer the following questions. (pp ) a) Chemical Equation: heat + H2(g) + O2(g) H2O2 (g) b) State what happens (in words) overall to the amounts of each reactant and product when hydrogen peroxide is added to the system at equilibrium? Stress: H2O2 added to system Response: Shift to left (products decrease, reactants increase) Change in amounts of reactants and products overall: Therefore, the amounts of H2 and O2 increase due to the shift and H2O2 increases overall due to stress (the shift decreases amount of H2O2 but not as much as the stress increased it). A. Use the equation in the corresponding problem in #8A to answer the following questions. (pp ) a) Chemical Equation: b) State what happens (in words) overall to the amounts of each reactant and product when oxygen is removed from the system at equilibrium? Stress: Response: Change in amounts of reactants and products overall: Xavier University of Louisiana 101

20 Chemistry 1020, Module 13 Using LeChatelier's Principle to Predict Qualitative Changes in Equilibrium (and Equilibrium Constant) as Stress is Applied: #2 (continued) 9. B. Use the equation in the corresponding problem in #8B to answer the following questions. (pp ) a) Chemical Equation: b) State what happens (in words) overall to the amounts of each reactant and product when dinitrogen oxide is added to the system at equilibrium? Stress: Response: Change in amounts of reactants and products overall: C. Use the equation in the corresponding problem in #8C to answer the following questions. (pp ) a) Chemical Equation: b) State what happens (in words) overall to the amounts of each reactant and product when water is removed from the system at equilibrium? Stress: Response: Change in amounts of reactants and products overall: D. Use the equation in the corresponding problem in #8D to answer the following questions. (pp ) a) Chemical Equation: b) State what happens (in words) overall to the amounts of each reactant and product when hydrogen chloride is removed from the system at equilibrium? Stress: Response: Change in amounts of reactants and products overall: E. Use the equation in the corresponding problem in #8E to answer the following questions. (pp ) a) Chemical Equation: b) State what happens (in words) overall to the amounts of each reactant and product when chlorine is removed from the system at equilibrium? Stress: Response: Change in amounts of reactants and products overall: F. Use the equation in the corresponding problem in #8F to answer the following questions. (pp ) a) Chemical Equation: b) State what happens (in words) overall to the amounts of each reactant and product when iodine is removed from the system at equilibrium? Stress: Response: Change in amounts of reactants and products overall: 102 Xavier University of Louisiana

21 Chemistry 1020, Module 13 Name Altering or Combining Equilibrium Reactions 10. Chemists often manipulate chemical equations. The following is intended to help you understand how the equilibrium expression (and constant) for a given equation is related to the equilibrium expression after that equation has undergone a variety of common manipulations. a) Reversing a chemical equation which is at equilibrium (615) Given the equation 1 N2(g) + 3 H2(g) 2 NH3(g), do the following: Write the chemical equation as given: The equilibrium expression for the equation as given: Write the chemical equation reversed: The equilibrium expression for the equation reversed: What is the relationship between the two equilibrium constants above? I.E. How does the equilibrium constant change when a reaction at equilibrium is reversed? (Kforward= 1/Kreverse) b) Multiplying an equation by a constant (615 Given the equation 1 N2(g) + 3 H2(g) 2 NH3(g), do the following: Write the chemical equation as given: The equilibrium expression for the equation as given: Multiply the chemical equation by 3: The equilibrium expression for the equation multiplied by 3: What is the relationship between the two equilibrium constants above? I.E. How does the equilibrium constant change when a reaction at equilibrium is multiplied by a constant (in this case 3 )? (K = K n ) Xavier University of Louisiana 103

22 Chemistry 1020, Module 13 Altering or Combining Equilibrium Reactions (continued) 10c) Adding two chemical equations Given the equations (1) H2S(aq) H + (aq) + HS - (aq) (2) HS - (aq) H + (aq) + S 2- (aq) do the following: Write the chemical equations as given: Write the equilibrium expressions for the equations to the left. Use K1 and K2 to distinguish between the two equilibrium constants. Add the two equations above together to obtain an overall equation: Write the equilibrium expression for the equation to the left. Label the equilibrium constant Koverall. What is the relationship between the three equilibrium constants above? I.E. How is the equilibrium constant of an equation obtained by adding two equations together related to the equilibrium constants for the original equations? (Koverall = K1*K2) d) How is the equilibrium expression of an equation obtained by subtracting one chemical equation from another related to the equilibrium expressions for the original equations? I.E. How would K1 and K2 be related to Koverall if you had subtracted equation 2 in c above from equation 1? (Note: subtracting equation 2 from equation 1 is the equivalent of reversing equation 2 and then adding to equation 1.) (Koverall = K1/K2reversed) 104 Xavier University of Louisiana

23 Chemistry 1020, Module 13 Name Altering or Combining Equilibrium Reactions (continued) 10e) Write the equilibrium expressions for the indicated equations, then combine them as indicated. Finally, indicate briefly how the equilibrium expression obtained is related to those for the original equations. S. Given equations: Equilibrium expressions: Eqn. 1: 2 CO(g) 2 C(s) + 1 O2(g) Expression 1: K1 = [O 2] [CO] 2 Eqn. 2: 2 CO(g) + 1 O2(g) [CO2] 2 2 CO2(g) Expression 2: K2 = [CO] 2 [O2] Combination: Reverse Eqn. 1 and add to Eqn. 2 Equation after combining: Equilibrium expression for combined equation: 2 C(s) + 1 O2(g) 2 CO(g) 2 CO(g) + 1 O2(g) 2 CO2(g) Expression 3: Kcombined = [CO 2] 2 [O2] 2 2 C(s) + 1 O2(g) + 2 CO(g) + 1 O2(g) 2 CO(g) + 2 CO2(g) <--Initial sum 2 C(s) + 2 O2(g) 2 CO2(g) <--Final sum Equation relating Expressions 1, 2, and 3: Kcombined = K 2 K1 = [CO2] 2 [CO] 2 [O2] * [CO]2 [O2] = [CO 2] 2 [O2] 2 A. Given equations: Equilibrium expressions: Eqn. 1: 2 SO2(g) + 1 O2(g) 2 SO3(g) Expression 1: Eqn. 2: 1 SO2(g) 1 S(s) + 1 O2(g) Expression 2: Combination: Reverse Eqn. 2 and add to Eqn. 1 Equation after combining: Equilibrium expression for combined equation: Expression 3: Equation relating Expressions 1, 2, and 3: Xavier University of Louisiana 105

24 Chemistry 1020, Module 13 Altering or Combining Equilibrium Reactions (continued) 10e) Write the equilibrium expressions for the indicated equations, then combine them as indicated. Finally, indicate briefly how the equilibrium expression obtained is related to those for the original equations. (p. 617) B. Given equations: Equilibrium expressions: Eqn. 1: 2 NO(g) + 1 O2(g) 2 NO2(g) Expression 1: Eqn. 2: 4 NO2(g) 2 N2O3(g) + 1 O2(g) Expression 2: Combination: Multiply Eqn. 1 by 2 and add to Eqn. 2 Equation after combining: Equilibrium expression for combined equation: Expression 3: Equation relating Expressions 1, 2, and 3: C. Given equations: Equilibrium expressions: Eqn. 1: 2 NO(g) + 1 O2(g) 2 NO2(g) Expression 1: Eqn. 2: 4 NO(g) 2 N2O(g) + 1 O2(g) Expression 2: Combination: Multiply Eqn. 1 by 2, then reverse Eqn. 2 and add the two together. Equation after combining: Equilibrium expression for combined equation: Expression 3: Equation relating Expressions 1, 2, and 3: 106 Xavier University of Louisiana

25 Chemistry 1020, Module 13 Name Altering or Combining Equilibrium Reactions (continued) 10e) Write the equilibrium expressions for the indicated equations, then combine them as indicated. Finally, indicate briefly how the equilibrium expression obtained is related to those for the original equations. (p. 615) D. Given equations: Equilibrium expressions: Eqn. 1: H2S(aq) HS - (aq) + H + (aq) Expression 1: Eqn. 2: H2S(aq) S 2- (aq) + 2 H + (aq) Expression 2: Combination: Reverse Eqn. 2 and then add to Eqn. 1 Equation after combining: Equilibrium expression for combined equation: Expression 3: Equation relating Expressions 1, 2, and 3: Bonding/Model Activity to Improve Ability to Visualize in 3-D S. a) Write the balanced equation if hypochlorous acid dissociates in water. HClO(aq) + H2O(l) ClO - (aq) + H3O + (aq) b) Draw the Lewis structure of all of the species in the above reaction. H O Cl + H O H [ ] - + [ ] + O Cl H O H A. a) Write the balanced equation if hydrogen chloride dissociates in water. H b) Draw the Lewis structure of all of the species in the above reaction. Xavier University of Louisiana 107

26 Chemistry 1020, Module 13 Bonding/Model Activity to Improve Ability to Visualize in 3-D (continued) B. a) Write the balanced equation if nitric acid dissociates in water. b) Draw the Lewis structure of all of the species in the above reaction. C. a) Write the balanced equation if ammonia reacts with water. (Note: Water donates an H + to the ammonia.) b) Draw the Lewis structure of all of the species in the above reaction. D. a) Write the balanced equation if acetic acid dissociates in water. b) Draw the Lewis structure of all of the species in the above reaction. 108 Xavier University of Louisiana

27 Chemistry 1020, Module 13 Name Bonding/Model Activity to Improve Ability to Visualize in 3-D (continued) E. a) Write the balanced equation if chlorous acid dissociates in water. b) Draw the Lewis structure of all of the species in the above reaction. A-E c) When you go to drill be prepared to assemble models of each of the reactants in the equations above and then use those models to demonstrate to your instructor what happens as the reactions occur. Challenge Questions A. In module 12 you learned that "like dissolves like." Therefore, when one mixes water (a polar substance) with CCl4 ( a nonpolar substance) the two do not mix but rather separate into two layers. If an organic substance, A, is now added to the mixture and it is shaken until equilibrium is reached, the substance A distributes itself between the two layers such that the equilibrium constant for the distribution is K = [A (water)]/[a (carbon tetrachloride)] = The equation for the distribution is A (carbon tetrachloride) A (water). If 10 grams of A are added to a mixture with milliliters of each water and carbon tetrachloride, how much A (in grams) would be in the carbon tetrachloride layer at equilibrium? B. For A, how many grams of A would be in the water layer if 50.0 grams of A were added to the mixture of ml of each water and CCl4? C. At a certain temperature, the equilibrium constant for the molecular rearrangement of 2,4-pentanedione to its enol form might be represented by 1 A 1 B, with an equilibrium constant If 0.10 moles of 2,4- pentandione (A) and 0.20 moles of the enol form is placed in ml of water, how much of the enol form (B) would be present when the system reaches equililbrium? D. At a certain temperature, the equilibrium constant for the molecular rearrangement of 2,4-pentanedione to its enol form might be represented by 1 A 1 B, with an equilibrium constant If 0.20 moles of 2,4- pentandione (A) and 0.30 moles of the enol form is placed in ml of water, how much of the enol form (B) would be present when the system reaches equililbrium? E. What is the equlibrium constant, Kc, for the reaction A 2 B if 5.0 moles of A are initially placed alone in a 3.0 L container and 6.0 moles of B are present at equilibrium? F. What is the equilibriuim constant, Kc, for the reaction 2 C 3 D if 12 moles of C and 5 moles of D are initially placed in a 5.0 L container and 14 moles of C are present at equilibrium? Xavier University of Louisiana 109

28 Chemistry 1020, Module 13 Note: All parts of this module as well as the following Skills Module on Quadratic Equations must be filled out when you arrive at drill. You will have quizzes on both. Revised: Mark Thomson 1997; Etim Eduok 2000; JWC 2001; JWC 2002; RI Xavier University of Louisiana