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Name _____________________________________________ Date ____________________ Class ____________________ 17 Chemical Equilibrium Reviewing Vocabulary Match the definition in Column A with the term in Column B. Column A Column B _______ 1. Equilibrium reaction in which the reactants and products are present in more than one physical state _______ 2. A state in which the forward and reverse reactions balance each other because they take place at equal rates _______ 3. An equilibrium constant for the dissolving of a sparingly soluble ionic compound in water _______ 4. An ion that is part of two or more ionic compounds in solution _______ 5. If a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. _______ 6. The numerical value of the ratio of product concentrations to reactant concentrations, with the concentration of each reactant and product raised to the power corresponding to its coefficient in the balanced equation a. reversible reaction b. common ion c. homogeneous equilibrium d. common ion effect e. chemical equilibrium f. equilibrium constant g. solubility product constant h. Le Châtelier’s principle i. law of chemical equilibrium j. heterogeneous equilibrium _______ 7. A reaction that can occur in both the forward and the reverse directions _______ 8. Equilibrium reaction in which all the reactants and products are in the same physical state _______ 9. At a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value. _______ 10. The solubility of a substance is lowered because of this. Answer the following question. 11. Explain the difference between the ion product (Qsp) and the solubility product constant (Ksp). ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ Chemistry: Matter and Change 1 Chapter Assessment Name _________________________________________ Date ____________________ Class ____________________________ 17 Understanding Main Ideas (Part A) Circle the letter of the choice that best completes the statement or answers the question. 1. This is the expression for the equilibrium constant for the reaction: CO(g) H2O(g) CO2(g) H2(g). a. Keq [CO][H 2O] b. K eq [CO2 ][H 2 ] [CO2 ][H 2 ] [CO][H 2O] c. Keq [CO2 ]2 [H 2 ] [CO][H 2O]2 d. K eq [CO 2 ][H 2 ] 2. The value of any equilibrium constant is correct only at a. a specific volume. c. a specific concentration. b. a specific pressure. d. a specific temperature. 3. What is indicated by a large value for Keq? a. A solution is saturated. b. Products are favored in the reaction. c. Reactants are favored in the reaction. d. The reaction is endothermic. 4. What predicts that increasing the concentration of NH3 will shift the following reaction to the left? N2(g) 3H2(g) 2NH3(g) a. Le Châtelier’s principle c. solubility product constant b. common ion effect d. law of chemical equilibrium 5. What will be the result if the volume of the reaction vessel is decreased for the reaction: H2(g) I2(g) 2HI(g)? a. The equilibrium shifts to the left. c. The equilibrium does not change. b. The equilibrium shifts to the right. d. The equilibrium constant changes. 6. The solubility product expression describes the equilibrium between a sparingly soluble ionic compound and a. the amount of substance added to solution. c. its ions in solution. b. the number of moles in the reaction. d. the equilibrium constant. 7. What can be determined if the ion product is compared to the solubility product constant? a. equilibrium c. the law of mass action b. whether a substance will precipitate d. the volume of the solution 8. What might cause the solubility of a substance to decrease? a. a decrease in temperature c. the presence of a common ion b. a decrease in pressure d. all of the above Chemistry: Matter and Change 2 Chapter Assessment Name _________________________________________ Date ____________________ Class ____________________________ 17 Understanding Main Ideas (Part B) For each reaction, describe how its equilibrium could be shifted in the indicated direction. 1. H2(g) Cl2(g) 2HCl(g) thermal energy: shift to the left ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 2. C(s) O2(g) CO2(g) thermal energy: shift to the right ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 3. Thermal energy 8SO2(g) S8(s) 16O2(g): shift to the right ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 4. PCl5(g) PCl3(g) Cl2(g) thermal energy: shift to the left ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ Making predictions Given the initial concentration of two ions, predict whether they will form a precipitate. Assume equal volumes of each solution have been mixed. 5. [Pb2] 0.700M; [F] 0.0500M; Ksp 3.3108 for PbF2 ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ Chemistry: Matter and Change 3 Chapter Assessment Name _________________________________________ Date ____________________ Class ____________________________ 17 Thinking Critically The graph shows how controlling the temperature and pressure of a reaction system changes the percent of product produced. 1. How does changing the pressure affect the amount of product produced? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 2. Is this reaction endothermic or exothermic? How do you know? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 3. If you needed to design an industrial reactor to produce the product from this reaction, what characteristics would you want it to have? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ Chemistry: Matter and Change 4 Chapter Assessment Name _________________________________________ Date ____________________ Class ____________________________ 17 Applying Scientific Methods When transporting food or other perishable items, more is involved than simply putting them into a package and sealing. Some perishable items can be sensitive to changes in temperature and humidity. If they are to stay fresh for the longest possible time, they need to be kept in a controlled environment. But, how can this be accomplished if they are traveling in a truck through different weather conditions? Also, when you receive your perishable product, how can you be certain that it has not been exposed to unfavorable conditions? It’s simple. You can use equilibrium. In water solutions, the Co 2 ion is pink. The pink color comes from the existence of the complex ion Co(H2O)62. When Cl ions are added to it, however, this ion converts by an endothermic reaction to Co(H2O)4Cl2, which is blue in aqueous solutions. These two species exist in equilibrium with each other. Use your scientific skills to determine how this behavior can be used to predict changes in temperature and humidity. 1. Write the balanced chemical equation for the endothermic equilibrium between the Co(H2O)62 and Co(H2O)2Cl2 species. Also, note the color of each of the cobalt species. (Hint: Use Cl.) ______________________________________________________________________________________________ 2. How would high humidity affect the equilibrium of the reaction? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 3. What effect would adding HCl have on the equilibrium? ______________________________________________________________________________________________ ______________________________________________________________________________________________ 4. How might a hot day affect the equilibrium of one of these cobalt packs? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ Chemistry: Matter and Change 5 Chapter Assessment Name _________________________________________ Date ____________________ Class ____________________________ 17 Applying Scientific Methods, continued 5. Packs containing Co(H2O)Cl2 are often placed in packages to protect the items inside from changes in humidity. Why does this work? What thing(s) might the pack have to do? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ 6. When the contents of a cobalt pack turn pink, does this mean the pack can no longer take up water? Why? What might allow the pack to take up more water? ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ ______________________________________________________________________________________________ Chemistry: Matter and Change 6 Chapter Assessment TEACHER GUIDE AND ANSWERS Chapter Assessment - Chapter 17 – Chemical Equilibrium 3. The reaction will shift to the right if the temperature is increased. It will also shift to the right if more SO2 is added or if O2 is taken away. Because S8 is a solid, it does not affect the equilibrium in any way. The reaction also will shift to the right if the volume is increased because there are more moles of gaseous product than of reactant. 4. The reaction will shift to the left if temperature is increased. It will shift to the left if the concentration of PCl3(g) or Cl2(g) is increased or if PCl5(g) is decreased. To shift the reaction to the left using pressure, decrease the volume. Making predictions Given the initial concentration of two ions, predict whether they will form a precipitate. Assume equal volumes of each solution have been mixed. 5. Answer: Divide each concentration by 2 Reviewing Vocabulary 1. j 2. e 3. g 4. b 5. h 6. f 7. a 8. c 9. i 10. d 11. The ion product is the product of the concentrations of the ions in a solution raised to the power equal to their coefficients. It may or may not be the solubility product constant. It equals the solubility product constant only if the solution is saturated. Qsp [Pb2][F–]2 [0.350][0.0250]2 (0.350)(6.2510–4) 2.1910–4. Because Qsp is greater than Ksp, a precipitate will form. Thinking Critically 1. Increasing the pressure reduces the amount of product produced as shown by the decrease in percent of product as pressure increases. Increasing the pressure means a decrease in the volume of the reaction vessel. The stress is relieved by shifting the equilibrium to the left because this decreases the total number of moles. 2. This reaction is exothermic because lowering the temperature increases the amount of product produced. Heat is a product of the reaction. Removing it by lowering the temperature causes the equilibrium to shift in the direction that produces heat, relieving the stress on the system. 3. Answers will vary. Answers should include running the reactor at low temperatures and reduced pressure to maximize the amount of product produced. They may also include some method of removing product as it is formed, which would favor its production by shifting the equilibrium of the reaction toward the products. Understanding Main Ideas (Part A) 1. b 2. d 3. b 4. a 5. c 6. c 7. b 8. d Understanding Main Ideas (Part B) 1. The reaction would go to the left if the temperature is raised. The left direction reaction uses heat and so relieves the stress. The left direction reaction will also be favored if HCl is added because the left reaction converts HCl to H2(g) and Cl2(g). Removing H2 or Cl2 also shifts the reaction to the left. 2. The reaction will shift to the right if the temperature is decreased. The right reaction relieves the stress. The reaction will also shift to the right if more O2(g) is added or if CO2 is taken away. Because C(s) is a solid, adding more of it will not change the equilibrium. This reaction is unaffected by changes in volume (i.e., same number of moles of gas on each side). Chemistry: Matter and Change Applying Scientific Methods 1. heat Co(H2O)62 (pink) 2Cl2 Co(H2O)4Cl2 (blue) 2H2O 2. When the humidity is high, there is a lot of water vapor in the air. The equation shows that adding water shifts the equilibrium to the left. In high 7 Teacher Guide and Answers TEACHER GUIDE AND ANSWERS humidity situations, therefore, the cobalt ion would dominate and the solution would have a pink color. 3. Hydrochloric acid has Cl– ions, which would force the equilibrium to the right and turn the solution a blue color. 4. We know that the reaction is endothermic. The hotter environment would place a stress on the system that would cause the reaction to shift to the right and the color would be blue. The right reaction takes up heat and so relieves the stress. 5. Answers may vary. If a pack containing Co(H2O)Cl2 is placed in a container, it will absorb some of the water from the air and make the air less humid. The equilibrium in the pack will be driven to the left. This will continue until equilibrium is achieved. The pack would have to be designed so that it collects water over a articular range of humidity conditions. This could be controlled by the quantity of chemicals in the pack. Chemistry: Matter and Change 6. Not necessarily; the pink color only means that the equilibrium has shifted far to the left. It does not mean that all the water that can be absorbed has been absorbed. Decreasing the temperature can make the pack take up more water. Because the reaction to the right is endothermic, the reaction to the left produces heat. When the temperature is decreased, the reaction to the left would dominate because it would produce heat that would relieve the stress placed upon the system. 8 Teacher Guide and Answers