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Gas Equilibria

Gas Equilibria. Unit 10. Equilibrium. Reactions are reversible Reactants are not consumed Equilibrium mixture containing both products and reactants is obtained. @ Equilibrium both (forward and reverse) reactions are taking place at the same time. Equilibrium.

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Gas Equilibria

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  1. Gas Equilibria Unit 10

  2. Equilibrium • Reactions are reversible • Reactants are not consumed • Equilibrium mixture containing both products and reactants is obtained. • @ Equilibrium both (forward and reverse) reactions are taking place at the same time.

  3. Equilibrium • The rate of the forward reaction = rate of the reverse reaction. • K = [products]^ coefficients [reactants]^ coefficients

  4. Equilibrium • K is the equilibrium constant; it shows the relationship between partial pressures of different GASES present at equilibrium • We need the partial pressure of each species • PV=nRT • Pressure must be in atms • R value will 0.0821 • V in L • T in Kelvins

  5. At equilibrium • Partial pressures remain constant as long as volume of container and temperature remain the same. • Kp is equilibrium using partial pressure • Kc represents concentration in moles/L (This is when we are looking at aqueous solutions and ions) • Kp= Kc(RT)∆ng ng= moles of gases

  6. At Equilibrium • For the most part, we are only going to be concerned about Kp so when asked to solve for K it is asking about Kp • When writing K expressions, you only include gases and aqueous solutions or ions.

  7. Writing K expressions • Let’s look at page 344 • #6 • #8 • #12 • HW#1

  8. Solving for Kc • N2 (g) + O2 (g) ↔ 2NO • Kp= 0.0255 • T= 123oC • Solver for Kc • On problems 37-40 you are just solving for Kc. Do not follow the directions. • HW#1

  9. Solving for K • N2 (g) + O2 (g) ↔ 2NO • P N2= 0.345 atm • P O2= 0.765 atm • P NO = 1.34 atm • HW#2

  10. Le Chatelier’s Principle • When a change (that is, a change in concentration, temperature, pressure, or volume, pH, etc) is imposed on a system at equilibrium, the system responds by attaining a new equilibrium condition that minimizes the impact of the imposed change. • I.e., the system will shift to undo the change

  11. Concentration • If you increase the concentration of any species, the reaction goes in the direction to get rid of it. (Solids, liquids=no effect) • A + B n C + D • Add A,  • Add C,  • Add E, since not in the equilibrium, no effect!

  12. Pressure • When the pressure of a system increases, to reduce the pressure the equilibrium will shift toward the side with the least moles of gases. • Decrease pressure, add more moles

  13. Volume • When the volume of the system increases, we need to fill it back up. The equilibrium will shift toward the side with more moles of gas. • Decrease volume, decrease moles.

  14. Temperature • The effect of temperature depends on the sign of DH. Treat temperature like a chemical: add heat, go to the cool side. • If DH is negative, products are exothermic (Hot side). • If DH is positive, products are endothermic (Cool side)

  15. Reaction Quotient • Q = [products]^ coefficients [reactants]^ coefficients This relationship can determine if a system is at equilibrium. It will also be used to predict direction to shift the system.

  16. Q vs K • If K < Q, the reaction R  P • Because for Q to be too large, there is presently too much product. To undo product, the reaction arrow shifts to make more reactant. Vice versa…. • If K > Q, the reaction R  P • Q is too small because there isn’t enough product.

  17. CO + 3H2n CH4 + H2O • Kp = 102 at 773 K • The following are introduced into a flask at 773K: 0.902 atm CO, 1.794 atm H2, 18.38 atm CH4 and 27.57 atm H2O. In what direction will the reaction occur to reach equilibrium?

  18. CO + 3H2n CH4 + H2O • Kp = 102 at 773K • The following are added to a 15.5 L reaction vessel at 773K: 25.2 g CO, 15.1 g H2, 130.2 g CH4 and 125 g H2O. In what direction will a net reaction occur to reach equilibrium?

  19. CO2 + CF4n 2COF2 • Kc = 0.50 at 1000oC • If a 2.50 L reaction vessel at 1000oCcontains 0.525 mol CO2, 1.25 mol CF4 and 0.75 mol COF2, in what direction will a net reaction occur to reach equilibrium? • HW#3

  20. I C E • When an equilibrium shifts, it MUST do so STOICHIOMETRICALLY! The coefficients determine the amount and the arrow determines the direction. • I -- Initial concentration or pressure • C --Change by coefficients • E -- Equilibrium is established

  21. CO + H2O n CO2 + H2 • Kp = 23.2 at 600K • If 0.250 mol of CO and H2O are introduced into a 1 L flask and equilibrium is established, how many moles of each will be present at equilibrium?

  22. C (s) + H2O n CO + H2 • Kp = 0.111 at 1100 K • If 0.100 atm H2O and 0.100 atm of H2 are mixed with excess carbon in a 1 L flask initially, what will be the equilibrium concentration of each?

  23. CO + Cl2nCOCl2 • The Kp = 21.88 at 395oC. • Initially, 20.0 g CO and 35.5 g Cl2 are placed in an 8.05 L reaction vessel at 395oC. What is the partial pressure of each at equilibrium?

  24. H2 + I2n 2HI • At 430oC, the Kc = 54.3. • A 1.0 L vessel is charged at this temperature with 1.4 atm of each. What is the partial pressure of each gas?

  25. CO2 + CF4n 2COF2 • The Kp at 1000oC is 0.50. • The vessel is charged initially with 0.45 atm of carbon dioxide and carbon tetrafluoride and 1.2 atm of COF2. What is the partial pressure of each gas?

  26. NO + CO2n NO2 + CO • Initially a vessel is charged with 3.9 moles of NO and 0.88 moles of CO2. At equilibrium, there is 0.11 mol of CO2. • What is the Kp? • What is Kc? • In another experiment, all gases are initially at 1.5 atm. What is the equilibrium pressure?

  27. Van’t Hoff Equation • Ln K2 – ln K1 = -∆H/R (T2-1-T1-1) • lnK2/K1= -∆/R(T2-1- T1-2) • R= 8.31 ∆H= Standard Enthalpy ∆G = -RTlnK ***Remember this,

  28. Van’t Hoff Equation • For the reaction, H2 + Br2 → 2HBr the Kp is 2.18 x 106 at 730oC. What is the Kp at 1000oC (you must calculate ∆H first)?

  29. Van’t Hoff Equation • The hydrogenation of octene to octane is an important process in refining gasoline. The K value for the reaction if 1.7 x 1015 at 298 K and is only 3.2 at 900K. • (a) What is the ∆H for this reaction? • (b) What is the∆G for this reaction at 298K?

  30. Adding Chemical Equations • Reaction 1= K1 • Reaction 2 = K2 • Reaction 3= K3 (overall reaction) • K3 = K1 * K2

  31. Adding Chemical Equations • Calculate K for the reaction: • SnO2 (s) + 2CO → Sn (s) + 2CO2 • Given • SnO2 (s) + 2H2 → Sn (s) + 2H2O K = 8.12 • H2 + CO2 → H2O + CO K = 0.771

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