1. Manipulating Equilibrium Constants

2. 1) Coefficient Rule If coefficients change in a chemical reaction to a certain “n” value, raise the K eq to the same “n” value Stoichiometric ratios remain in the same proportion

3. Example 1: A) 2A + B  6D Kc = [D] 6 [A] 2 [B] B) A + ½ B  3D (Kc) 1/2 = [D] 3 OR [A] 2 [B] 1/2 (Kc) 1/2 = [ [D] 6 /[A] 2 [B] ] 1/2

4. 2) Reciprocal Rule The K eq value for a reverse reaction is the INVERSE of the forward K eq value 1/K eq = K eq for reverse reaction

5. Example 2: A) 2A + B  6D Kc = [D] 6 [A] 2 [B] B) 6D  2A + B Kc = [A] 2 [B] [D] 6 Kc for reverse = 1/Kc

6. 3) Multiple Equilibria Rule If the overall chemical reaction is broken into multiple steps and then combined……. Overall K eq = product of K eq values from each chemical reaction

7. Example 3: 2A + B  6D #1 K eq 3E + B  2A + F#2 K eq __________________________________________________________________ 3E + 2B  6D + F Total K eq = (#1K eq )(#2K eq )

8. Le’Chatlier’s Principle

9. Basic Concept Main concept in chemical equilibrium Change in a variable that alters the equilibrium of a system (chemical reaction) products a shift in the OPPOSITE direction Reaction shifts to counteract the variable’s influence Reaction tries to get back to equilibrium state-----SO reaction shifts

10. Basic Concept (cont.) What happens to a chemical reaction when equilibrium shifts When one side of a chemical reaction is stressed, the reaction shifts to the side of LEAST stress !

11. Variables disrupting equilibrium 1) Addition or removal of chemical compounds from the reaction. 2) Pressure 3) Temperature/Heat

12. 1) Concentration Changes Addition of a chemical compound Reactions shifts towards opposite side to reduce the effect of this addition Removal of a chemical compound Reaction shifts towards the production of compound to reduce the effect of removing it. Equilibrium constant (Kc) remains the same

13. 2) Pressure Changes Focus on stoichiometric ratios in chemical reaction Reaction shifts in a direction aimed to REDUCE pressure change Increased pressure Reaction will shift to side with LESS gas particles to reduce pressure Decreased pressure Reaction will shift to side with MORE gas particles to increase pressure Equilibrium constant (Kc) remains the same

14. 3) Temperature Changes Increased temperature Reaction shifts AWAY from increased temperature since temperature is forcing more product to be made Similar to adding more product to a reaction Decreased temperature Slowing production of product, stress removed from forward reaction Reaction shifts TOWARDS decrease in temperature Equilibrium constant (Kc) does NOT remain the same Changes with temperature

15. Example 4: A + B  AB  Heat A  Cool B  Add AB  Take out B

16. Example 5: Predict the influence of certain changes to the following chemical reaction. 2SO 3(g)  2SO 2(g) + O 2(g) ΔH°= 197.84 kJ/mol A) increasing reaction’s temperature B) increasing reaction’s pressure C) adding more O 2 at equilibrium D) Removing O 2 at equilibrium

17. Homework Due Friday ! ! Equilibrium II Worksheet LeChatlier Problem Worksheet