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Class Demo with hall

Definition. Class Demo with hall Chemical Equilibrium – when the rate of the forward and reverse reactions are equal Dynamic – Reactions at eq never stop Equilibrium DOES NOT mean that the amount of reactants and products are equal. They have reached an unchanging ratio. Definition.

marny-anderson
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Class Demo with hall

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  1. Definition Class Demo with hall • Chemical Equilibrium – when the rate of the forward and reverse reactions are equal • Dynamic – Reactions at eq never stop • Equilibrium DOES NOT mean that the amount of reactants and products are equal. They have reached an unchanging ratio

  2. Definition Equilibrium GI

  3. Cis Trans

  4. Definition • NaCl (s)  Na+(aq) + Cl-(aq) [unsaturated] • NaCl (s) Na+(aq) + Cl-(aq) [saturated]

  5. Graphs N2O4(g)  2NO2(g) Clear Brown Cold Hot • Starting with all reactants (N2O4) N2O4(g)  2NO2(g) 2. Starting with all products (NO2)

  6. Eq. Constants • Kc = Eq. Constant involving molarity a. Molarity = [ ] b. Example = [0.50 M] 2. Kp = Eq. Constant involving pressure a. Atmospheres b. We live at about 1 atm • Generic Example aA + bB  cC + dD

  7. Eq. Constants 2O3(g)  3O2(g) 2NO(g) + Cl2(g)  2NOCl(g) H2(g) + I2(g)  2HI(g)

  8. Heterogeneous Equilibrium • More than one state is present • Exclude solids and liquids from K. (not considered to have a molarity or pressure)

  9. Heterogeneous Eq. SnO2(s) + 2CO(g)  Sn(s) + 2CO2(g) Pb(NO3)2(aq)+Na2SO4(aq)PbSO4(s) +2NaNO3(aq) Ba2+(aq) + SO42-(aq)  BaSO4(s)

  10. A Note About Water • Exclude liquid water (often the solvent) • Keep gaseous water • Examples CO2(g) + H2(g)  CO(g) + H2O(l) 3Fe(s) + 4H2O(g)  Fe3O4(s) + 4H2(g)

  11. An example CO(g) + Cl2(g)  COCl2(g) Kc = 4.6 X 109 • Rules K>>1 Favors the products K<<1 Favors the reactants K~1 Reactants ~ Products

  12. Does the following reaction favor the products or reactants? N2(g) + O2(g)  2NO(g) Kc = 1 X 10-30 • For the following reaction, Kc = 794 at 298 K and Kc = 54 at 700 K. Should you heat or cool the mixture to promote the formation of HI? H2(g) + I2(g)  2HI(g)

  13. Kc= 2.5 X 10-30 for N2(g) + O2(g)  2NO(g) calculate Kc for: 2NO(g) N2(g) + O2(g) • Calculate Kc for ½ N2(g) + ½ O2(g)  NO(g) 3. The Kc for N2(g) + 3H2(g)  2NH3(g) is 4.43 X10-3. Calculate Kc for: 2N2(g) + 6H2(g)  4NH3(g)

  14. Converting Between Kc and Kp Kp = Kc (RT)Dn R = 0.0821 L atm/mol K T = Kelvin Temperature Dn = change in number of moles of gas

  15. Calculate Kp for the following reaction at 300 oC: N2(g) + 3H2(g)  2NH3(g) Kc = 9.60 ANS: 0.00434 (4.34 X 10-3)

  16. Calculate Kp for the following reaction at 1000 K: 2 SO3(g)  2SO2(g) + O2(g) Kc = 4.08 X 10-3 ANS: 0.335

  17. A mixture is allowed to reach eq.. At eq., the vessel contained 0.1207 M H2, 0.0402 M N2, and 0.00272 M NH3. Calculate the equilibrium constant. N2(g) + 3H2(g)  2NH3(g) (Ans: 0.105)

  18. 2. At eq., a vessel contained 0.00106 M NO2Cl, 0.0108 M NO2, and 0.00538 M Cl2. Calculate the equilibrium constant. NO2Cl(g) NO2(g) + Cl2(g) (Ans: 0.558)

  19. 3. A mixture of 0.00500 mol of H2 and 0.0100 mol of I2 is placed in a 5.00 L flask and allowed to reach eq.. At eq., the mixture is found to be [HI] = 0.00187 M. Calculate Kc. H2(g) + I2(g)  HI(g) (Ans: 51)

  20. 4. A vessel is charged with 0.00609 M SO3. At eq., the SO3 concentration had dropped to 0.00244 M SO3. What is the value of Kc? SO3(g)  SO2(g) + O2(g) (Ans: 0.0041)

  21. 5. 4.00 mol of HI was placed in a 5.00 L flask and allowed to decompose. At eq. It was found that the vessel contained 0.442 mol of I2. What is the value of Kc? HI(g)  H2(g) + I2(g) (Ans: 0.020)

  22. An eq. mixture of gases is analyzed. The partial pressure of nitrogen is 0.432 atm and the partial pressure of hydrogen is 0.928 atm. If Kp is 1.45 X 10-5, what is the partial pressure of ammonia? N2(g) + 3H2(g)  2NH3(g)

  23. Consider the following equilibrium: PCl5(g)  PCl3(g) + Cl2(g) • At equilibrium, the partial pressure of PCl5 and PCl3 are measured to be 0.860 atm and 0.350 atm, respectively. If Kp = 0.497, what is the partial pressure of Cl2? (1.22 atm) • Suppose at equilibrium the partial pressure of PCl5 is 2.00 atm. Calculate the partial pressure of PCl3 and Cl2 . Assume Kp is still 0.497 and only PCl5 was initially in the flask. (0.997 atm)

  24. 0 = ax2+ bx + c • x = -b + \/ b2 – 4ac 2a • 2x2 + 4x = 1

  25. 1. A gas cylinder is charged with 1.66 atm of PCl5 and allowed to reach eq.. If the Kp= 0.497, what are the pressures of all the gases at equilibrium? PCl5(g)  PCl3(g) + Cl2(g) (Ans: 0.97 atm, 0.693 atm)

  26. 2. A 1.000 L flask is filled with 1.000 mol of H2 and 2.000 mol of I2. The Kc = 50.5. What are the concentrations of all the gases at equilibrium? H2(g) + I2(g)  2HI(g) (Ans: 0.065 M, 1.065 M, 1.87 M)

  27. Do I always need the quadratic, or can I cheat? The equilibrium constant for the following reaction is 2400. 2NO(g)  N2(g) + O2(g) If the initial concentration of NO is 0.157 M, calculate the equilibrium concentrations of NO, N2 and O2. (Ans: 0.0016 M, 0.0777 M, 0.0777 M)

  28. Q: Reaction Quotient • Reaction Quotient • Calculated the same as K, but using initial concentrations 3. Q < K shifts to products Q = K at equilibrium Q > K shifts to reactants

  29. If you introduce 0.0200 mol of HI, 0.0100 mol of H2 and 0.0300 mol of I2 in a 2.00 L flask, which way will the reaction proceed to reach equilibrium? H2(g) + I2(g)  2HI(g) Kc = 51 (Ans: Q = 1.3)

  30. 2. Predict which way the following reaction will proceed as it reaches eq. Assume that you start with [SO3] = 0.002 M, [SO2] = 0.005 M and [O2] = 0.03M. 2SO3(g)  2SO2(g) + O2(g) Kc = 0.0041 (Ans: Q = 0.2)

  31. Predict which way the following reaction will proceed as it reaches eq. Assume that you start with [NH3] = 0.002 M, [N2] = 0.005 M and no H2. Kc= 0.105 N2(g) + 3H2(g)  2NH3(g)

  32. LeChatelier’s Principle Blue Bottle Demo 5 grams KOH 3 grams Dextrose 250 mL of water 1 drop methylene blue

  33. Le’Chatelier’s Principle LeChatelier’s Principle • Definition – If a system at eq. Is disturbed, it will shift to relieve that disturbance If a system at eq. is disturbed, it will shift to relieve that disturbance

  34. N2(g) + 3H2(g)  2NH3(g) • Add N2 • Add NH3 • Remove NH3 as it forms • Remove H2 N.B. Does NOT apply to solids and liquids. They do not appear in the K. LiCl(s)  Li+(aq) + Cl-(aq)

  35. Disturbing and K • Adding products = K increases (TEMPORARILY) • Adding reactants = K decreases (TEMPORARILY) N2(g) + 3H2(g)  2NH3(g) Kc = [NH3]2 [N2][H2]3

  36. N2(g) + 3H2(g)  2NH3(g) • Identify the # of moles of gas on either side. • Show piston drawing • Increase the volume of the container • Decrease the volume of the container

  37. N2(g) + 3H2(g)  2NH3(g) • Increase the pressure of the system • Decrease the pressure of the system Soda example (CO2(aq)  CO2(g)) N.B. Adding a noble or inert gas has no effect on the eq. Pressure change without a volume change.

  38. Endothermic Reactions – absorb heat from the surroundings • Heat is added (reactants) • Cooking is an example DH + • Exothermic Reactions – Release heat • Give off heat (products) • Fire is an example DH -

  39. CO(g) + 3H2(g)  CH4(g) + H2O(g) DH = -206 kJ/mol • Heat the system • Cool the system

  40. Catalyst • Examples a. Enzymes b. Vitamins c. Catalytic convertor 3. No effect on the position of equilibrium

  41. Example 1 N2O4(g)  2NO2(g) DH = 58 kJ/mol • Add N2O4 • Remove NO2 as it forms • Increase the total pressure • Increase the total volume • Cool the solution • Add a catalyst

  42. Example 2. 2PbS(s) + 3O2(g)  2PbO(s) + 2SO2(g) DH = -37 kJ/mol • Add PbS • Remove SO2 as it forms • Add O2 • Increase volume • Decrease the pressure • Heat the flask

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