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| Understanding the concepts
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Check your answers |
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| 1.a.
| To review the collision model, open the Transition States and Activation Energy Understanding Concepts on the CD and read the Introduction and Example. (Click through the screens of the Example using the arrow buttons.) Why does the rate of a reaction generally increase when the concentration of reactants increases?
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| b.
| Why does the rate of a reaction increase when the temperature increases? How does a catalyst speed up a reaction?
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| 2.a.
| Open the Equilibrium Decomposition of N2O4 Visualization on the CD and read the concept. Equilibrium is a dynamic process. What does this mean? For a reaction at equilibrium, what is true about the rate of the forward and reverse reactions and what is true about the concentrations of reactants and products? For the reaction N2O4(g)  2 NO2(g), what is the equilibrium constant expression (K)? |
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| b.
| When temperature is constant, the value of K for a reaction is a constant value. We often say that the value of K is independent of the amounts of reactants and products that are mixed together initially. Explain this statement. What is an equilibrium position? For help answering these questions, open the Results of Three Experiments Table on the Web site.
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| c.
| The value of K does change when the temperature changes. For some reactions, K increases as temperature increases while for other reactions, K decreases as temperature increases. Look closely at the Equilibrium Decomposition of N2O4 Visualization on the CD. From the animation, did the value of K increase or decrease as temperature increased? Hint: Compare the amount of NO2 and N2O4 present at equilibrium before and after the heating. |
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| 3.a.
| For practice writing K expressions, do Problems 16.16 and 16.18 in the text.
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| 3.b.
| What is heterogeneous equilibria? What is different between writing K expressions for heterogeneous equilibria versus a reaction where all reactants and products are in the gaseous state? For practice writing K expressions for heterogeneous equilibria, do Problems 16.26 and 16.28 in the text.
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| 4.a.
| For practice with equilibrium calculations, do Problems 16.46, 16.48, 16.50, and 16.52 in the text.
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| b.
| A special type of equilibrium discussed in the text is solubility equilibria. For some substance, what reaction does solubility equilibria refer and what is Ksp? Use Ag3PO4(s) to illustrate your answers to the previous questions. For practice writing Ksp expressions, do Problem 16.58 in the text.
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| c.
| Two typical calculations involving solubility equilibria are: 1. Given the Ksp value for an ionic compound, calculate the solubility for the compound. 2. Given the solubility, calculate the Ksp value. To practice these types of calculations, do Problems 16.60, 16.64, 16.65, 16.67, 16.68, and 16.70 in the text.
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| 5a.
| What is Le Chatelier's Principle? When a reactant or product is added, the reaction shifts to reestablish equilibrium. Does the value of K change when a reactant or product is added? Consider the N2O4(g) 2 NO2(g) equilibria. Predict the effect on the equilibrium position when N2O4 added, when N2O4 is removed, when NO2 is added, and when NO2 is removed. Check your answers by reviewing the Shifts in the Equilibrium Position Table. For a more difficult problem on predicting the effect of concentration changes, do Problem 16.36 (a-d) in the text.
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| b.
| Another typical stress applied to reactions is changing the volume of the reaction container. Does the value of K change when the container volume is changed? Consider the reaction N2O4(g) 2 NO2(g). If the volume of the container is decreased or increased, what effect does this have on the equilibrium position? Open the "Shifts in the Equilibrium Position" Table on the Web site to check your answers.
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| c.
| The final type of stress addressed in the text is the effect of temperature on the equilibrium position. To predict the effect of a temperature change, you must know whether a reaction absorbs heat or releases heat when reactants are converted to products. Is heat a product or a reactant in an exothermic reaction? How about an endothermic reaction? To see an example of an exothermic reaction, view the Thermite Reaction Visualization on the CD; to see an example of an endothermic reaction, view the Ammonium Chloride and Barium Hydroxide Visualization on the CD. For an exothermic reaction, does the reaction shift left or right when the temperature is decreased? For an endothermic reaction, does the reaction shift left or right when the temperature is increased?
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| d.
| Open the Chemical Equilibrium Understanding Concepts on the CD and read the Introduction to review Le Chatelier's Principle. Next, go through the example, which examines the Fe3+ + NCS- FeNCS2+ equilibrium. The Exercises study the effect of adding several reagents to this equilibrium. Your job is to use Le Chatelier's principle to predict which way the reaction shifts with each reagent added. It's important to know the color of solution when the hydrated Fe3+ dominates and the color of solution when FeNCS2+ dominates. What color is each of these species?
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| e.
| Go through all eight exercises in the Understanding Concepts above and predict which way the reaction shifts to reestablish equilibrium. Also predict the color change that should occur. Play the reaction to verify your answer and then view the detailed explanation. This is an excellent exercise, so go through all of the choices. The effects that some of the reagent additions have are not obvious. Here are some hints to help you deduce what should happen: Addition of tin(II) chloride: Sn2+ reacts with Fe3+ to produce Sn4+ and Fe2+. Addition of silver nitrate: Ag+ reacts with NCS- to produce solid AgNCS. Addition of sodium hydrogen phosphate: HPO42- reacts with Fe3+ to produce FeHPO4+. Addition of ammonia: The weak base NH3 produces OH- which reacts with Fe3+ to produce solid Fe(OH)3. Addition of heat: The reaction is exothermic.
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| 6.
| Open Key Words on the CD and test your ability to define important terms presented in Chapter 16.
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| 7.
| Test your understanding of Chapter 16 by taking the ACE quizzes on the Web site.
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