Reaction Rate and Equilibrium Chapter 19 Assignment & Problem Set

Transcription

1 Reaction Rate and Equilibrium Name Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8.

2 Reaction Rate and Equilibrium 2 Study Guide: Things You Must Know Vocabulary (know the definition and what it means): rate of reaction collision theory molecular orientation during a collision potential energy and kinetic energy potential Energy diagram activation energy transition state or activated complex catalyst and inhibitor endothermic and exothermic heat of reaction or enthalpy reversible reaction equilibrium (both chemical and physical) and the extent of a reaction Honors: equilibrium constant (K eq) LeChatelier s principle stress to an equilibrium thermodynamics spontaneous and nonspontaneous reaction entropy and randomness Honors: Gibbs free energy Learning Objectives: factors that influence the rate of a reaction. collision theory. how to draw, label and interpret potential energy diagrams including: determining the heat of a reaction determining whether a reaction is endo- or exothermic calculating the activation energy of the forward and reverse reaction. how to determine the heat of a reaction using Table I. how a catalyst and inhibitor affect the rate of a reaction. what is meant by a reversible reaction. Honors: how to calculate the equilibrium constant for a chemical reaction. Honors: how to determine whether there are mostly reactants or products at equilibrium given K eq. how to determine shifts in equilibrium due to changes in concentration, pressure, volume, and temperature using Le Chatelier s principle. factors that determine entropy. how to determine whether a chemical reaction is spontaneous or nonspontaneous by evaluating enthalpy and entropy. Honors: how to calculate Gibbs free energy to determine whether a chemical reaction is spontaneous or nonspontaneous. Key Reference Tables Table I: Heats of Reaction at kpa and 298 K

3 Reaction Rate and Equilibrium 3 Read Chapter 19: Reaction Rate and Equilibrium. All students skip entropy calculations and free-energy calculations (pp ) and rate law & reaction mechanisms (pp ). Lab 20: Equilibrium & LeChatelier s Principle Regents Table I: Heats of Reaction Warm-ups and problems will be collected before you take the test. Answer all problems in the space provided. For problems involving an equation, carry out the following steps: 1. Write the equation. 2. Substitute numbers and units. 3. Show the final answer with units. There is no credit without showing work. Collision Theory 1. What is meant by rate of a chemical reaction? 2. Define activation energy. 3. Define collision theory? 4. Does every collision between reacting particles lead to products? Explain. 5. Draw a potential energy diagram (potential energy vs. reaction progress) for the reaction below. On your diagram, be sure to label both axes. Draw a vertical double-arrow showing the energy of the reactants, the energy of the products, the activation energy, and H. CO(g) + NO 2(g) CO 2(g) + NO(g) H = -54 kcal 6. For the reaction in the above problem, how much heat is released when 25 grams of NO are produced? 7. Sketch an energy profile curve (potential energy diagram) for the gas-phase reaction shown below. The reaction has an activation energy of 22 kj, and the total energy change ( H) is -103 kj. F(g) + H 2(g) HF(g) + H(g)

4 Reaction Rate and Equilibrium 4 8. For the reaction A + B C, the activation energy of the forward reaction is 5kJ and the total energy change is -20kJ. What is the activation energy of the reverse reaction? 9. How does each factor affect the rate of a chemical reaction (increase or decrease)? a. temperature b. concentration c. particle size d. catalyst 10. Refrigerated food stays fresh for long periods. The same food stored at room temperature quickly spoils. Why? 11. Where is the formula of a catalyst written in a chemical equation? Why? 12. The reaction of hydrogen and oxygen gas to produce water is very slow at room temperature but occurs with explosive rapidity in the presence of a flame or ignition wire. Explain. Chemical Equilibrium and the Equilibrium Constant 13. What is the significance of double arrows in an equation? 14. Define chemical equilibrium. How do the rates of the forward and reverse reactions compare at equilibrium? 15. How do the amounts of reactants and products change once a reaction has achieved chemical equilibrium? 16. Give two examples of physical equilibria. 17. Honors Write the expression for the equilibrium constant for each reaction. a. 4H 2(g) + CS 2(g) CH 4(g) + 2H 2S(g) b. 2NO(g) + O 2(g) 2NO 2(g) 18. Honors Imagine you have determined the following equilibrium constants for several reactions. State which of these reactions favor products and which favor reactants? a. K eq = 1 x 10 2 b. K eq = c. K eq = 3.5 d. K eq = 6 x 10-4

5 Reaction Rate and Equilibrium Honors Analysis of an equilibrium mixture of nitrogen, hydrogen, and ammonia contained in a 3.0 L flask at 300 o C gives the following results: 0.15 mol hydrogen; 0.25 mol nitrogen; 0.10 mol ammonia. Calculate K eq for the reaction: N 2(g) + 3H 2(g) 2NH 3(g) 20. Honors Suppose the following system reaches equilibrium at a high temperature. N 2(g) + O 2(g) 2NO(g) An analysis of the equilibrium mixture in a 0.50 L flask gives the following results: nitrogen, 0.50 mol; oxygen, 0.50 mol; nitrogen monoxide, mol. Calculate K eq for the reaction. 21. Honors For the following reaction at equilibrium at 827 o C, the following amounts were determined: mol CO 2, mol H 2, mol CO and mol H 2O. What is the value of K eq? CO 2(g) + H 2(g) CO(g) + H 2O(g). Chemical Equilibrium and LeChatelier s Principle 22. Define LeChatelier s Principle. 23. How is the equilibrium position (right or left) of this reaction affected by the following changes? C(s) + H 2O(l) + heat CO(g) + H 2(g) a. lowering the temperature b. decreasing the pressure c. removing H 2 d. adding H What would be the effect on the equilibrium position (shift to products or reactants) if the volume were decreased in each reaction? a. 4HCl(g ) + O 2(g) 2Cl 2(g) + 2H 2O(g) b. CO 2(s) CO 2(g) c. CaCO 3(s) CaO(s) + CO 2(g)

6 Reaction Rate and Equilibrium How does the equilibrium shift (right or left) in the reaction below? N 2(g) + 3H 2(g) 2NH 3(g) a. if the pressure is increased b. if volume is increased c. if heat is added d. if a catalyst is added e. if the temperature is decreased f. if ammonia is removed 26. Honors Is eating sugar candy really bad for your teeth? Tooth decay is the result of the dissolving of tooth enamel (Ca 3(PO 4) 3OH). In the mouth the following equilibrium is established. Ca 3(PO 4) 3OH 5Ca +2 (aq) + 3PO 4-3 (aq) + OH - (aq) When sugar ferments on teeth, H + is produced. What effect does increased H + have on tooth enamel? Explain 27. Honors The freezing of liquid water at 0 o C can be represented as follows: H 2O(l,d=1.00g/cm 3 ) H 2O(s,d = 0.92g/cm 3 ) where d = density. Explain why the application of pressure causes ice to melt. Thermodynamics 28. Define spontaneous reaction. 29. What two factors determine whether a reaction is spontaneous? 30. Define entropy and enthalpy. 31. Which system has the lower entropy? a. completed jigsaw puzzle or separate jigsaw pieces b. 50 ml of liquid water or 50 ml of ice c. 10g of sodium chloride crystals or a solution containing 10 g of sodium chloride d. a solid at 30 o C or the same solid at 400 o C e. clean water or dirty water

7 Reaction Rate and Equilibrium Predict the direction of the entropy change (increase or decrease?) in each reaction. a. CaCO 3(s) CaO(s) + CO 2(g) b. 2NH 3(g) + HCl(g) NH 4Cl(s) c. 2NaHCO 3(s) Ca 2CO 3(s) + H 2O(l) + CO 2(g) d. C(s) + O 2(g) CO 2(g) 33. Describe how entropy and enthalpy are related in predicting whether a reaction is spontaneous. 34. Use Regents Table I and your prediction of entropy change to predict whether the following reaction is spontaneous: N 2(g) + 2O 2(g) 2NO 2(g) 35. Is it true that all spontaneous processes are exothermic? Explain your answer. 36. Honors What single thermodynamic quantity tells you if a reaction is spontaneous? How? 37. Honors What is the equation relating entropy and enthalpy to free energy? 38. Honors For the reaction: 2NO(g) + O 2(g) 2NO 2(g) predict whether this reaction is spontaneous at -100 o C and at +800 o C given that H =-27.4 kcal and S = cal/k. Review 39. What is wrong with saying that solid potassium chloride is composed of KCl molecules? 40. Name the following compounds and give the charge on the anion for each. a. NaClO 4 b. Ca 3(PO 4) 2 c. Na 2SO 4 d. SnO e. MgCO 3 f. K 2Cr 2O 7