Notes

Outline

Equilibrium Competency 9 Review

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

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

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

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

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

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.

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]

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

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.

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.

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.

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.

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.

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.

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