CHEM 1332 CHAPTER 14

Transcription

1 CHEM 1332 CHAPTER Which is a proper description of chemical equilibrium? The frequencies of reactant and of product collisions are identical. The concentrations of products and reactants are identical. The velocities of product and reactant molecules are identical. Reactant molecules are forming products as fast as product molecules are reacting to form reactants. The numbers of moles of reactants and products are equal 2. Chemical equilibrium is the result of a decrease in speed of reaction. the unavailability of one of the reactants. a stoppage of further reaction. opposing reactions attaining equal speeds. formation of products equal in mass to the reactants. 3. The value of the equilibrium constant K for a reaction at equilibrium is altered by changing the temperature. adding a catalyst. adding water. changing the effective concentration of reactants. changing the effective concentration of products. 4. When a chemical system is at equilibrium, the concentrations of the reactants are equal to the concentrations of the products the forward and reverse reactions have stopped the reaction quotient, Q, has reached a maximum the concentrations of the reactants and products have reached constant values none of these 5. Which of these statements is NOT TRUE? the equilibrium constant is independent of temperature a system that is disturbed from an equilibrium condition responds in a manner to restore equilibrium equilibrium is molecular systems is dynamic, with two opposing processes balancing each other the value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium is attained a system evolves spontaneously toward a state of equilibrium 6. What is the equilibrium constant expression (K c ) for the gas phase oxidation of CO to CO 2 by means of O 2? [CO 2 ] 2 K = [CO] [O 2 ] [CO 2 ] 2 K = [CO] 2 [O 2 ] K = [CO]2 [O 2 ] [CO 2 ] K = [CO] [O 2] [CO 2 ] 1

2 7. Calculate Kp for H 2 O(g) + ½ O 2 (g) H 2 O 2 (g) at 600 K using the following data: H 2 (g) + O 2 (g) H 2 O 2 (g) Kp = 2.3 x 10 6 at 600 K 2 H 2 (g) + O 2 (g) 2 H 2 O(g) Kp = 1.8 x at 600 K 2.6 x x x x x For the aqueous reaction, A + 2 B 3 C + 4 D, I mix 1 mole of A, 2 moles of B, 1 mole of C and 2 moles of D in a 1 L container. If the equilibrium constant (K c ) at this temperature is 5, then the reaction mixture is at equilibrium the reaction will proceed to the left the reaction will proceed to the right none of these are correct the [products] will be MUCH smaller than the [reactants] at equilibrium 9. The equilibrium constant (K c ) for the gaseous reaction, C + D E + 2F, is 3.0 at 50 C. In a 2.0 L flask at 50 C are placed 1.0 mol of C, 1.0 mol of D, 1.0 mol of E, and 3.0 mol of F. Initially, the reaction will proceed at equal rates in both directions. proceed more rapidly to form E and F. proceed more rapidly to form C and D. not occur in either direction. 10. The equilibrium constants, K c and K p, will equal each other when: all of the reactants and products are gases the number of moles of gaseous products is greater than the number of moles of gaseous reactants the number of moles of gaseous products is less than the number of moles of gaseous reactants the number of moles of gaseous products is equal to the number of moles of gaseous reactants they are never equal to each other 11. K p at 25 C for the reaction, NO 2 (g) NO(g) + O 2 (g) is 4.48 x Calculate the value for K c x x x x 10-9 cannot be determined 12. Consider the exothermic reaction: N 2 (g) + 3H 2 (g) 2NH 3 (g) ΔH = 92.1 kj. At 400 K, the equilibrium constant (K c ) is Calculate K p for the reaction at 400 K x Nitric oxide and bromine were allowed to react in a sealed container, according to the equation, NO(g) + Br 2 (g) NOBr(g). At equilibrium, p(no) = atm, p(br 2 ) = 1.59 atm, and p(nobr) = 7.68 atm. Calculate K p for the reaction x Calculate K c for the reaction, N 2 (g) + 3H 2 (g) 2NH 3 (g) when the equilibrium concentration moles per liter are: N 2 = 0.02, H 2 = 0.01, NH 3 = x x x x

3 15. A 1.20-L flask contains an equilibrium mixture of mol of N 2, mol of H 2, and mol of NH 3. Calculate K c for the reaction N 2 (g) + 3H 2 (g) 2NH 3 (g) Under a set of equilibrium conditions [HI] = 0.10 M and [H 2 ] = [I 2 ]. Calculate the concentration of I 2 if the equilibrium constant (K c ) = HI(g) H 2 (g) + I 2 (g) 1.3 x10 2 M 3.1 x 10 1 M 4.0 x 10 2 M 1.3 M 17. Given the equilibrium equation, A 2 + B 2 2AB. At 25 C, the equilibrium concentrations in moles per liter are [A 2 ] = 0.40; [B 2 ] = 0.40; [AB] = What is the value of the equilibrium constant (K c )? The equilibrium constant (K c ) for the reaction, 2HBr(g) H 2 (g) + Br 2 (g) is 10 at a certain temperature, when concentrations are expressed in moles per liter. Calculate the number of moles of HBr(g), present at equilibrium if 100 L of the equilibrium mixture contain 5 mol of H 2(g) and 8 mol of Br 2(g) l For the reaction, CO(g) + Cl 2 (g) COCl 2 (g), K c = 5.1 x 10 9 at a particular temperature. Pure COCl 2 is added to a 1 liter flask. At equilibrium, it is found that 0.25 moles of COCl 2 remain. What is the equilibrium concentration of CO? 1.4 x 10-5 M 7.0 x 10-6 M 4.9 x M 0.75 M none of these 20. At a certain temperature, mol of PCl 5 was placed into a L vessel and permitted to react as shown. At equilibrium, the container held mol of PCl 5. What is the value of K c? PCl 5 (g) PCl 3 (g) + Cl 2 (g) One mole of a compound AB reacts with one mole of a compound CD according to, AB + CD AD + CB. When equilibrium has been established it is found that 0.75 mol of each of the reactants AB and CD has been converted to AD and CB. There is no change in volume. What is the equilibrium constant (K c ) for the reaction? 1/9 9 9/16 16/9 22. Consider the reaction: PCl 5 PCl 3 (g) + Cl 2 (g). At a particular temperature, 0.84 moles of PCl 5 is placed into a 1 L flask. At equilibrium, 0.72 moles of PCl 5 are present. Calculate K c for the reaction

4 23. Into an empty vessel COCl 2 (g) is introduced at 1.0 atm pressure whereupon it dissociates until equilibrium is established according to, 2COCl 2 (g) C(graphite) + CO 2 (g) + 2Cl 2 (g). If x represents the partial pressure of CO 2 (g) at equilibrium, what is the value of the equilibrium constant, K p? 2x 3 /(1.0 2x) 2 2x 4 / (1.0 2x 2 ) 4x) 3 /(1.0 2x) 2 4x 3 / (1.0 x) For the reaction, AB 3 (g) A(g) + 3B(g), what is the equilibrium constant expression if the initial concentration of AB 3 is 0.1 M and the concentration of A is represented by x? 3x 2 / (0.1 x ) x 4 / (0.1 x) 3 x 4 / (0.1 3x) 3 27x 4 / (0.1 x) 25. A mixture of 0.60 mol Cl 2 (g) and 0.40 mol F 2 (g) was allowed to come to equilibrium in a 1000 ml flask. If 2x represents the molar concentration of ClF(g) at equilibrium, which expression represents the equilibrium constant? Cl 2 (g) + F 2 (g) 2ClF(g) x 2 / [(0.60 x)(0.40 x)] 4x 2 / [(0.60 x)(0.40 x)] 2x / [(0.60 x)(0.40 x)] 2x 2 / [(0.60 x)(0.40 x)] 26. The equilibrium constant K p for the conversion, butane(g) isobutane(g), is 2.54 at 25 C. If butane at 1.00 atm is allowed to come to equilibrium, the partial pressure of isobutane in the equilibrium mixture will be atm 1.65 atm atm 2.54 atm 27. Consider the vapor phase reaction, 2 HCl H 2 + Cl 2, for which K c = 16 at 523 K. If moles of HCl is introduced into a 1 L vessel at 523 K, what is the equilibrium concentration of H 2? M M M 0.24 M M 28. The aqueous reaction, HN 3 + H 2 O N H 3 O + has a value of K c of 1.9 x What is the equilibrium concentration of H 3 O + in a solution which was initially 0.35 M HN 3? 3.89 x x x x x A mixture of 2.0 mol of CO(g) and 2.0 mol of H 2 O(g) was allowed to come to equilibrium in a l L flask at a high temperature. If K c = 4.0, what is the molar concentration of H 2 (g) in the equilibrium mixture? CO(g) + H 2 O(g) CO 2 (g) + H 2 (g) The equilibrium constant (K c ) for the reaction, 2HI(g) H 2 (g) + I 2 (g) is Calculate the number of moles of hydrogen produced when one mole of HI is placed in a 1 L vessel

5 31. At 80 C, K p for the reaction, N 2 O 4 (g) 2 NO 2 (g) is 4.66 x We introduce moles of N 2 O 4 into a 1.0 L vessel at 80 C and let equilibrium be established. The total pressure in the system at equilibrium will be: 0.23 atm 1.3 atm 2.3 atm 0.79 atm 32. In which reaction will an increase in total pressure at constant temperature favor formation of the products? CaCO 3 (s) CaO(s) + CO 2 (g) H 2 (g) + Cl 2 (g) 2HCl(g) 2NO(g) + O 2 (g) 2NO 2 (g) COCl 2 (g) CO(g) + Cl 2 (g) 33. Consider the gaseous reaction 2SO 2 + O 2 2SO 3 + heat. Under which conditions is SO 3 most stable? high pressure and high temperature high pressure and low temperature low pressure and high temperature low pressure and low temperature 34. Which of the following equilibria would be shifted toward the products by a decrease in the volume of the reaction vessel? H 2 (g) + I 2 (g) 2HI(g) 2N 2 O 5 (g) 4NO 2 (g) + O 2 (g) N 2 (g) + 3H 2 (g) 2NH 3 (g) NH 4 Cl(s) NH 3 (g) + HCl(g) 35. For the reaction, 2SO 2 (g) + O 2 (g) 2SO 3 (g) ΔH = 198 kj carried out at constant volume, the concentration of O 2 at equilibrium will increase if: SO 2 is added to the system. SO 3 is added to the system. the temperature of the system is lowered. the volume is decreased 36. For the reaction, 2SO 2 (g) + O 2 (g) 2SO 3 (g), carried out at constant temperature and volume, what is the effect of removing some SO 3 from a system initially at equilibrium? [SO 2 ] decreases more than [O 2 ]. [SO 2 ] increases more than [O 2 ]. [SO 2 ] and [O 2 ] remain the same. [SO 2 ] and [O 2 ] decrease equally. 37. The equilibrium, PCl 5 (g) PCl 3 (g) + Cl 2 (g), will be shifted to the right by the addition of a catalyst. removal of Cl 2. increase of pressure removal of PCl In the reaction, heat + CaSO 3 (s) CaO(s) + SO 2 (g), which change will cause an increase in the amount of SO 2 (g) when equilibrium is re-established? increasing the reaction temperature adding some more CaSO 3 decreasing the volume of the container removing some of the CaO(s) 5

6 39. Which factor would cause a change in the equilibrium constant, K c, for this reaction? 2NOCl(g) 2NO(g) + Cl 2 (g) adding NO(g) decreasing the volume of the reaction vessel cooling the system removing NO(g) 40. In which gaseous reaction would an increase in pressure at constant temperature have no effect on the relative amounts of the substances present in the equilibrium mixture? 2NO + O 2 2NO 2 + heat heat + N 2 + O 2 2NO N 2 + 3H 2 2NH 3 + heat 2CO + O 2 2CO 2 + heat heat + N 2 O 4 2NO If the system, H 2 (g) + I 2 (g) 2HI(g) is initially at equilibrium, the amount of HI present in the equilibrium mixture at constant temperature could be increased by increasing [H 2 ] adding a catalyst. increasing the pressure lowering [I 2 ] increasing the volume 42. Given the exothermic reaction:, N 2 (g) + 3H 2 (g) 2NH 3 (g) ΔH = 92.1 kj. At 400 K, the equilibrium constant (K c ) is At 800 K, what is the value of the equilibrium constant? 0.53 > 0.53 < 0.53 dependent on [NH 3 ] 43. Consider the gas reaction, 2 NH 3 N H 2, for which ΔH = kj. If, when this reaction is at equilibrium, N 2 (g) is added: the concentration of NH 3 will decrease the concentration of H 2 will increase the value of K c will increase the reaction will shift to the right the same thing as would have happened if the temperature had been lowered will happen 44. For the endothermic reaction, CaCO 3 (s) CaO(s) + CO 2 (g), which of the following actions would shift the equilibrium to form more CO 2 gas? increasing the temperature decreasing the temperature increasing the pressure increasing both the pressure and temperature increasing the pressure and decreasing the temperature 45. Consider the following system at equilibrium: N 2 (g) + 3 H 2 (g) 2 NH 3 (g), ΔH = kj. Which of the following changes will shift the equilibrium to the right? 1. increasing the temperature 2. Decreasing the temperature 3. increasing the volume 4. Decreasing the volume 5. removing some NH 3 6. Adding some NH 3 2,4,5 1,4,6 2,3,5 1,6 1,3,5 ANSWERS: D D A D A C E C C D B E D C B A E D B C B B C D B C B D D C D C B C B A B A C B A C E A A 6