6. Which will react faster: Magnesium and 2M hydrochloric acid, or Magnesium and 0.5M hydrochloric acid?

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1 REACTION RATES WORKSHEET WS#1 1. Identify the three components of collision theory. What are the three factors that must be true for a collision to be successful? a. b. c. 2. Do all collisions result in a chemical reaction? Explain. 3. Identify the four factors that will affect the rate of reaction. Explain how they affect the rate of reaction. Use a molecular picture as part of your explanation. a. b. c. d. 4. Why does increasing temperature speed up a chemical reaction? Use collision theory to explain your answer. 5. Hydrogen and iodine react at 400 o C, according to the equation, H2(g) + I2(g) 2HI (g). How would the rate of reaction be affected by the following: a) increasing the temperature b) increasing the concentration of iodine c) increasing the concentration of both the hydrogen and the iodine d) adding a catalyst 6. Which will react faster: Magnesium and 2M hydrochloric acid, or Magnesium and 0.5M hydrochloric acid? 7. Use collision theory to explain why increasing the concentration of hydrochloric acid would cause an increase in the rate of its reaction with zinc.

2 8. Which will burn faster: a solid log, or wood shavings? 9. Using collision theory explain the following: a) Sugar dissolves faster in a cup of hot tea than in ice tea. b) A sugar cube dissolves more slowly than table sugar. c) Stirring a teaspoon of sugar helps it dissolve faster than not stirring it. 10. The diagram below shows that a reaction is taking place. This is an effective collision. State 2 reasons why. 11. The following collisions do NOT react. State why. a. b. c. 12. Why does a certain mass of iron filings rust faster than an iron nail? 13. Using collision theory, explain how a catalyst speeds up a reaction. 14. It has been observed that more gas station fires occur on hot days than on cold days. Explain this phenomenon using your knowledge of collision theory. (Hint: It s not just the temperature increase that causes this!)

3 Understand activation energy and interpret energy graphs. 1. Define the following terms: a. Activation energy -E a b. Activated complex c. Catalyst WS#2 2. Use the potential energy diagram for the reaction A + B -> C + D to answer the following questions. a. Is the reaction exothermic or endothermic? b. What is the value of H? c. What is the value of the activation energy of the reaction? d. What is the potential energy of the products? e. What is the potential energy of the activated complex? 3. Use the potential energy diagram for the reaction to answer the following questions. a. Is the reaction exothermic or endothermic? b. What is the value of the activation energy of the uncatalyzed reaction? c. What is the value of the activation energy of the catalyzed reaction? d. What is the potential energy of the activated complex of the catalyzed reaction? e. How does the H for the catalyzed reaction compare to H for the uncatalyzed reaction? They are exactly the same (20 kcal). The addition of the catalyst does not change the heat of the reaction ( H) it only changes the activation energy.

4 4. For each potential energy graph below: a. Label: reactants, products, activated complex, activation energy, change in enthalpy ( H) b. Find the activation energy for the forward and the reverse reaction. c. Find the H for the forward and the reverse reaction d. Label each as exothermic or endothermic. 5. N 2 + 3H 2 2NH kJ a. Is this reaction exothermic or endothermic? b. Sketch a potential energy diagram. 6. Draw an energy diagram for a reaction. (label the axis) potential energy of reactants = 350 kj/mole Activation energy = 100 kj/mole Potential energy of products = 250 kj/mole Is the reaction in # 6 exothermic or endothermic? Explain.

5 Equilibrium 1. Define dynamic chemical equilibrium. WS#3 2. Based on the definition of equilibrium: a. What is equal at equilibrium? b. What remains constant at equilibrium, but does not have to be equal? 3. Write the equilibrium expression, K eq, for each of the following reactions a. 2 NO (g) + O 2(g) 2 NO 2(g) b. 4 HCl (g) + O 2(g) 2 H 2O (g) + 2 Cl 2(g) c. NOCl (g) NO (g) + ½ Cl 2(g) d. CaCl 2(s) Ca 2+ (aq) + 2Cl - (aq) e. HC 2H 3O 2(aq) + H 2O (l) H 3O + (aq) + C 2H 3O 2 - (aq) f. MgO (s) + CO 2(g) MgCO 3(s) 4. Classify the following equilibria as heterogeneous or homogeneous, and write an equilibrium expression for each. a) NH 4NO 2(s) N 2(g) + 2 H 2O (g) b) H 2O (l) H 2O (g) c) SO 2(g) + ½ O 2(g) SO 3(g) d) S 8(s) + 8 O 2(g) 8 SO 2(g) 5. Calculate the equilibrium constant (Keq ) for the following balanced equations and state whether the reaction favors the products or the reactants. a. PCl 5(g) PCl 3(g) + Cl 2(g) At the equilibrium point in the decomposition of phosphorus pentachloride to chlorine and phosphorus trichloride, the following concentrations are obtained: mol/l PCl 5, 0.15 mol/l PCl 3 and 0.37 mol/l Cl 2. K eq = Products or reactants?

6 b. CO 2 (aq) + 2 H 2O (l) HCO 3 - (aq) + H 3O + (aq) A solution at equilibrium contains 0.500M CO 2, 0.225M HCO 3 -, M H 3O + K eq = Products or reactants? c. SO 3 (g) + H 2O (g) H 2SO 4 (l) A solution at equilibrium contains 1.20 M SO 3, M H 2O, and 4.20 M H 2SO 4 K eq = Products or reactants? d. 2 KBr (aq) + SrO (aq) K 2O (aq) + SrBr 2 (aq) A solution at equilibrium contains M KBr, 0.056g SrO, 1.23 M K 2O, and 0.23 mol SrBr 2 in a 1.00 L container. K eq = Products or reactants? 6. The dissociation of acetic acid, CH 3COOH, has an equilibrium constant at 25 C of 1.8 x The reaction is CH 3COOH (aq) CH 3COO - (aq) + H + (aq) If the equilibrium concentration of CH 3COOH is 0.46 moles in L of water and that of CH 3COO - is 8.1 x 10-3 moles in the same L, calculate [H + ] for the reaction. [H + ] = 7. 4 HCl (g) + O 2 (g) 2 H 2 O (l) + 2 Cl 2 (g) K eq = 3.62 x 10-3 A solution at equilibrium contains mol HCl, mol O 2, and mol H 2O in a ml container. Calculate the concentration of chlorine gas [Cl 2] =

7 Le Chatelier s Principle WS#4 Le Chatelier s Principle states that when a system at equilibrium is subjected to a stress, the system will shift its equilibrium point in order to relieve the stress. Directions: For each gaseous system at equilibrium, indicate what happens to the equilibrium position when the indicated stress is applied. Tell whether the reaction shifts toward the Left or Right or if there is No Effect. 1. N2 + 3H2 2NH3 + heat a. remove ammonia gas b. decrease volume 2. CO2 + H2 + heat CO + H2O a. decrease temperature b. add a catalyst 3. 2SO2 + O2 2SO3 + heat a. increase sulfur dioxide concentration b. increase temperature 4. CO2 + C + heat 2CO a. increase temperature b. increase carbon monoxide concentration 5. N2O4 + heat 2NO2 a. decrease volume b. remove dinitrogen tetroxide 6. In this reaction: 2 NO (g) + H 2 (g) N 2 O (g) + H 2 O (g) + heat What will happen to the [H2O] when equilibrium is reestablished after these stresses are applied? a. temperature is increased d. NO is added b. a catalyst is added e. N 2O is removed c. pressure is decreased 7. How would an increase in pressure affect the [H 2] in the following reactions? 2 H 2 (g) + O 2 (g) 2 H2 O (g) 4 H 2 (g) + Fe 3 O 4 (s) 3 Fe (s) + 4 H 2 O (l) H 2 (g) + Cl 2 (g) 2 HCl (g) 8. 2NH3(g) + heat N2(g) + 3H2(g) Stress Equilibrium Shift [NH3] [N2] [H2] 1. Add nitrogen 2. Add hydrogen 3. Add ammonia 4. Remove nitrogen 5. Remove hydrogen 6. Remove ammonia 7. Decrease volume

8 H2(g) + I2(g) + heat 2HI(g) Stress Equilibrium Shift [H2] [I2] [HI] 1. Add hydrogen 2. Add iodine 3. Add HI 4. Remove hydrogen 5. Remove iodine 6. Remove HI 7. Increase temperature 8. Decrease temperature 9. Increase volume 10. Decrease volume 9. Fe(OH) 2 (aq) + AlCl 3 (aq) FeCl 2 (aq) + Al(OH) 3 (s) + heat Change Shift Effect on Increase [AlCl3] [FeCl2] Add aluminum hydroxide [Fe(OH)2] Remove FeCl2 [AlCl3] Add catalyst [Fe(OH)2] Cool it down (remove heat) [AlCl3] 10. For the reaction below, which change would cause the equilibrium to shift to the right? CH4 (g) + 2H2S(g) CS2(g) + 4H2(g) (a) Decrease the concentration of H2S (b) Increase the pressure on the system. (c) Increase the temperature of the system. (d) Increase the concentration of CS2 (e) Decrease the concentration of methane. f) Adding a catalyst

9 Reaction rates and Equilibrium 1. The diagram represent the changes in potential energy that occur during the given reaction. Review Sheet Given the reaction: A + B C a. Is the above reaction endothermic or exothermic reaction? State one reason, in terms of energy, to support your answer b. Draw a dashed line on the diagram to indicate a potential energy curve for the reaction if a catalyst is added. 2. The diagram represents the potential energy changes when a cold pack is activated. 3. a. The heat content of the reactants of the forward reaction is about kilojoules. b. The heat content of the products of the forward reaction is about kilojoules. c. The heat content of the activated complex of the forward reaction is about kilojoules. d. The activation energy of the forward reaction is about kilojoules. e. The heat of reaction ( H) of the forward reaction is about kilojoules. f. The forward reaction is (endothermic or exothermic). g. The heat content of the reactants of the reverse reaction is about kilojoules. h. The heat content of the products of the reverse reaction is about kilojoules. i. The heat content of the activated complex of the reverse reaction is about kilojoules. j. The activation energy of the reverse reaction is about kilojoules. k. The heat of reaction ( H) of the reverse reaction is about kilojoules. l. The reverse reaction is (endothermic or exothermic). a. Catalysts are substances that reactions by providing an pathway for the breaking and making of bonds. Key to this alternative pathway is a energy than that required for the reaction. b. Industrial chemical plants employ catalysts daily to make huge quantities of common products, such as acetic acid. Platinum, palladium and rhodium($100,000/g) are all used but are very expensive metals and indeed each is more expensive than gold. How can it be economically worthwhile to use such expensive compounds in the production of everyday materials? 4. Why is Advil sold as a soluble gel capsule containing the powdered active ingredient, rather than just a solid tablet? 5. Equilibrium is dynamic: Explain

10 6. Pure and are not included in the equilibrium expression because 7. Interpreting the magnitude of Keq a. When Keq > 1 the reaction is favored b. When Keq < 1 the reaction is favored 8. Calculate the equilibrium constant for the reaction 2ICl(g) <==> I 2(g) + Cl 2(g) when the following concentrations are measured: [ICl]=2.5 M, [I 2] =2.0 M, [Cl 2]= 1.2 M. Are the reactants or products favored? 9. For the reaction, 2SO 2(g) + O 2(g) 2SO 3(g), the equilibrium concentrations of the sulfur oxides are [SO 2] = 2.00 and [SO 3] = What is the equilibrium concentration of oxygen when Keq is for the reaction? 10. Indicate shifts by telling what happens to the amount of reactants and products as a result of shift left and right. 2NO(g) + O 2(g) 2NO 2(g) + heat Stress Results Shitft Increases Decreases a. Increase concentration of O 2 b. Decrease concentration of NO 2 c. Increase volume d. Decrease volume e. Increase temperature f. Decrease temperature For the following reaction 5 CO(g) + I2O5(s) ) <==> I2(g) + 5 CO2(g) kj For each change listed, predict the equilibrium shift and the effect on the indicated quantity. Change Direction of Shift Effect on Quantity (a) increase in pressure [CO 2(g)] Effect (increase, decrease, or no change) (b) raise temperature [CO(g)] (e) removal of I2(g) [ CO2(g)] 11. The following reaction shows the manufacture of ethyl alcohol CH 2=CH 2(g) + H 2O(g) CH 3CH 2OH(g) + 46 kj (ethene) (ethyl alcohol) a. To get the maximum yield of ethanol a low temperature is needed. Explain why. b. A high pressure is favored in order to convert ethane in ethyl alcohol Explain. Why. c. Would adding heat favor the production of ethanol? d. This reaction is performed at very high temperature (300ºC). Use your knowledge of kinetics to explain why lower temperatures are not used.