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Le Chatelier’s Principle review

Le Chatelier’s Principle review. If a stress is applied to a system at equilibrium, the position of the equilibrium will shift to reduce the stress. 3 Types of stress. Change Pressure. By changing volume System will move in the direction that depends on the # moles of gas.

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Le Chatelier’s Principle review

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  1. Le Chatelier’s Principle review • If a stress is applied to a system at equilibrium, the position of the equilibrium will shift to reduce the stress. • 3 Types of stress

  2. Change Pressure • By changing volume • System will move in the direction that depends on the # moles of gas. • Because partial pressures (and concentrations) change a new equilibrium must be reached. • System tries to minimize the moles of gas.

  3. Change in Pressure • By adding an inert gas • Partial pressures of reactants and product are not changed • No effect on equilibrium position

  4. Change in Temperature • Affects the rates of both the forward and reverse reactions. • Doesn’t just change the equilibrium position, changes the equilibrium constant. • The direction of the shift depends on whether it is exo- or endothermic

  5. Exothermic • DH<0 • Releases heat • Think of heat as a product • Raising temperature push toward reactants. • Shifts to left.

  6. Endothermic • DH>0 • Produces heat • Think of heat as a reactant • Raising temperature push toward products. • Shifts to right.

  7. Determine the effect on the equilibrium in the following: Consider: 2SO2 (g) + O2 2SO3(g) H <0 a) Adding SO2 • temp. is increased • Volume of container is increased • Catalyst is added • An inert gas is added

  8. Shifts to the right • Shifts to the left • Pressure decreases for all the gases; affects left side more- shifts to the left • No effect; equilibrium is reached faster. • Total pressure is increased; partial pressures of the individual gases is unaffected.

  9. Determine the effect on the equilibrium in the following: Consider: H2O(g) + heat 2H2 (g) + O2(g) a) Adding H2 • temp. is increased • Volume of container is decreased • Catalyst is added • An inert gas is added

  10. a).shifts to the left b).shifts to the right c) pressure increases for all the gases; effect is greater on product side- shifts to the left. d).no effect; equilibrium is reached sooner. e) Total pressure is increased; partial pressures of the individual gases is unaffected.

  11. Equilibrium Constant Calculations

  12. Calculate K N2 + 3H2 2NH3 Initial At Equilibrium [N2] =1.000 M [N2] = 0.921M [H2] =1.000 M [H2] = 0.763M [NH3] =0 M [NH3] = 0.157M

  13. Keq=[NH3]2 [H2 ]3 [N2 ] =[0.157M]2 [0.763M ]3 [0.921M ] = 6.03 x 10-2M-2

  14. Calculate K N2 + 3H2 2NH3 Initial At Equilibrium [N2] = 0 M [N2] = 0.238 M [H2] = 0 M [H2] = 1.197 M [NH3] = 1.000 M [NH3] = 0.157M K is the same no matter what the amount of starting materials

  15. Keq=[NH3]2 [H2 ]3 [N2 ] =[0.157M]2 [1.197 M ]3 [0.238 M ] = 6.03 x 10-2M-2

  16. Equilibrium and Pressure • Some reactions are gaseous • PV = nRT • P = (n/V)RT • P = CRT • C is a concentration in moles/Liter • C = P/RT

  17. Equilibrium and Pressure • 2SO2(g) + O2(g) 2SO3(g) • Kp = (PSO3)2 (PSO2)2 (PO2) • K = [SO3]2 [SO2]2 [O2]

  18. Equilibrium and Pressure • K =(PSO3/RT)2 (PSO2/RT)2(PO2/RT) • K =(PSO3)2 (1/RT)2 (PSO2)2(PO2) (1/RT)3 • K = Kp (1/RT)2= Kp RT (1/RT)3

  19. AP enrichment General Equation • jA + kB lC + mD • Kp= (PC)l (PD)m= (CCxRT)l (CDxRT)m (PA)j (PB)k (CAxRT)j(CBxRT)k • Kp=(CC)l (CD)mx(RT)l+m (CA)j(CB)kx(RT)j+k • Kp =K (RT)(l+m)-(j+k) = K (RT)Dn • Dn=(l+m)-(j+k)=Change in moles of gas

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