1. Shifting Equilibrium

2. Applications Involving the Equilibrium Constant
The Meaning of K
K > 1  the equilibrium position is far to the right
K < 1  the equilibrium position is far to the left

3. The value of K for a system can be calculated from a known set of equilibrium concentrations.
Unknown equilibrium concentrations can be calculated if the value of K and the remaining equilibrium concentrations are known.

4. Le Chatelier’s Principle
A reaction at equilibrium will proceed in a direction that relieves the stress put on it.
The equilibrium position changes, but the equilibrium constant (K) does not change unless temperature changes

5. Factors that “stress” or shift the Equilibrium
Temperature - ↑ temp = ↑ reaction rate
Only thing that changes K because it affects the free energy of the reaction!
If exothermic, a temperature ↑ will make rxn proceed to the left (to reactants)
If endothermic, a temperature ↑ will make rxn proceed to the right (to products)

6. Volume Look at the number of moles of gas
↓ the volume ↑ the pressure, & will cause the reaction to proceed towards the side with fewer moles of gas
↓ volume ↑ reaction rate for both the forward & reverse reactions.
The side with more moles of gas has an advantage since there are more collision per unit of time
Changing volume does not change K

7. Pressure Look at the number of moles of gas
Pressure can be changed 2 ways
Changing volume (see previous slide); changing pressure this was does change reaction rate
Adding an inert gas; changing pressure this was does NOT change reaction rate
Changing pressure does not change K

8. Concentration Look at the reactants & products
If reactant’s concentration ↑, reaction shifts towards products
If product’s concentration ↑, reaction shifts towards reactants

9. Can change concentration by:
Adding reactant or product
Removing reactant or product
Adding something that complete (or almost completely) reacts with the reactant or products
If you add something that forms a precipitate with one the reactants or products, you are effectively removing that reactant or product

10. Example: 2H2(g) + O2(g) + energy ↔ 2H2O(g)
If [H2] increases, reaction will shift to the because more product will be made to use up the excess H2
If [H2] decreases, reaction will shift to the to make up some of the H2 that was lost

11. Example: 2H2(g) + O2(g) + energy ↔ 2H2O(g)
Is this reaction endothermic or exothermic?
If temp. increases, reaction will shift to the energy is a reactant, will shift right to use up the added energy
If temp. decreases, reaction will shift to the energy is a reactant, will shift left to make up the energy that is being lost
When pressure ↑, & volume ↓, reaction shifts to make fewer moles of gas
When pressure ↓, & volume ↑, reaction shifts to make more moles of gas