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Equilibrium

Equilibrium. Competency 9 Review. Calculating K c. Given [concentration] of all species Write the K c expression Fill in the expression accordingly Solve for K c. Calculating K c. Given (original concentration) of one species and [EC] of another Write the Kc expression

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Equilibrium

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  1. Equilibrium Competency 9 Review

  2. Calculating Kc • Given [concentration] of all species • Write the Kc expression • Fill in the expression accordingly • Solve for Kc

  3. Calculating Kc • Given (original concentration) of one species and [EC] of another • Write the Kc expression • Set up chart filling in what you know • Figure out change: [EC] – (OC) • Determine change for all species • Calculate [EC] for each species • Fill in the expression accordingly • Solve for Kc

  4. Calculating Kc • Given (original concentration) of one species and how much of it was used • Write the Kc expression • Set up chart filling in what you know • Figure out change: (OC) x % of change • Determine change for all species • Calculate [EC] for each species • Fill in the expression accordingly • Solve for Kc

  5. Using Kc • OCQ: Original Concentration Quotent • Use OCQ to determine direction of the rxn when (OC) for all species is given • If OCQ > Kc rxn • If OCQ < Kc rxn

  6. Using Kc • Given Kc and [concentration] of all species except one. • Write the Kc expression • Fill all known values into the expression and solve for the unknown

  7. Using Kc • Given Kc and only the (OC) for all species • Set up chart filling in what you know • Let “x” represent the change – determine the direction of the rxn if necessary (Use OCQ) • Let “x” be negative on the side reacting and positive on products side.

  8. Using Kc • Given Kc and only the (OC) for all species (continued) • Multiply “x” by coefficients in the equation for that species • Substitute the [OC +/- change] as [EC] value and solve for “x” • Substitute value of “x” to get actual [EC]

  9. LeChatelier’s Principle: • When a system at equilibrium is subjected to a stress, the system will shift in a direction so as to relieve the stress. • What are some of these “stresses”? • Adding or subtracting a species • change in volume of the container • change in the pressure • change in the temperature

  10. LeChatelier’s Principle: • Adding a species. • Rxn will shift in the direction away from the species added. • Removing a species. • Rxn will shift in the direction toward the species removed.

  11. LeChatelier’s Principle: • Changing the volume of the container. • Increase in the volume. • Rxn will shift toward the side with the most moles of gas. • Decreasing the volume. • Rxn will shift toward the side with the fewest moles of gas. • Changing the volume will make no difference if there are the same number of moles of gas on each side.

  12. LeChatelier’s Principle: • Changing the pressure on the container. • Increase in the pressure. • Rxn will shift toward the side with the fewest moles of gas. • Decreasing the pressure. • Rxn will shift toward the side with the most moles of gas. • Changing the pressure will make no difference if there are the same number of moles of gas on each side.

  13. LeChatelier’s Principle: • Changing the temperature. • Affect determined by sign of DH • New value for Kc also a result • Increase in temperature shifts the reaction in the endothermic direction • Decrease in temperature shifts the reaction in the exothermic direction.

  14. Kc and Kp • Kp is the equilibrium constant based on equilibrium partial pressures in atm. • It is related to Kc by the equation: • Kp = Kc(RT)Dng where R is the Ideal Gas Constant and T is the temperature. Dng is the change in number of moles of gas as the reaction is read, left to right. In other words, # mol of gas products - # mol of gas reactants.

  15. Relationship between DG and K • Mathematical relationship is: DG = -0.0191 T logK • K stands for every equilibrium constant used in different types of equilibria. It applies to Kp and NOT Kc for gaseous equilibria.

  16. K versus the sign of DG • If DG < 0, then log K > 0 and K > 1 • when all species are at unit concentrations the reaction is spontaneous to the right. • If DG > 0, then log K < 0 and K < 1 • the reaction is spontaneous to the left • If DG = 0, then log K = 0 and K = 1 • the reaction is at equilibrium

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