1. THE EQUILIBRIUM CONSTANT CHAPTER 18 PAGES 555-559
Chemistry

2. Review
Consider the following reaction and indicate if the statements below are true or false.
2SO2(g) + O2(g) ↔  2SO3(g)
At the beginning of the reaction before equilibrium, there are more reactants than products
At equilibrium, the reverse rate of reaction is greater than the forward since there is only one product
At equilibrium, the forward and reverse reaction rates are equal

3. Review
Consider the following reaction and indicate if the statements below are true or false.
2SO2(g) + O2(g) ↔  2SO3(g)
At equilibrium, the concentrations of reactants and products are exactly the same
After equilibrium is reached, the reactions stop since the equilibrium is dynamic
After equilibrium, if the conditions are suitable, then all of the reactants will be converted to products

4. Equilibrium Constant
Why would we want to know the concentrations of the reactants and products at equilibrium?
Simply put… if the concentrations of reactants and products are known, then reaction conditions can be changed to maximize product formation
So how can we find this information?

5. Equilibrium Constant
To determine the equilibrium constant, we have to look at the balanced chemical equation
Lets look back to our review example
2SO2(g) + O2(g) ↔  2SO3(g)
After equilibrium is reached, the concentrations of the reactants and product should remain constant; so a ratio of their concentrations should also be constant

6. Equilibrium Constant
The equilibrium constant is designated by the letter Keq
To find the Keq, it is simply the concentration of the products in the numerator, each raised to a power equal to the coefficient of that substance in the chemical equation. The concentration of the reactants are in the denominator, each raised to a power equal to the coefficient of that substance in the chemical equation.
NOTE: Pure solids and liquids are left out since the concentrations will not change (For example: H2O(l))

7. Equilibrium Constant Lets look back to our review example
2SO2(g) + O2(g) ↔  2SO3(g)
What is the Keq?

8. Value of the Equilibrium Constant
So I can find Keq…But what does it really mean?
Again, the Keq helps determine the product yield
What would be favorable for our product yield?
Three different situations that can occur with Keq … lets look at them

9. Value of the Equilibrium Constant
Value of Keq
Forward vs. Reverse Reaction
Reactants or Products Favored
Low
Forward reaction occurs only very slightly
Reactants favored
Equal to 1
Forward and reverse reactions equal
Roughly equal concentrations of reactants and products
High
Reverse reaction occurs only very slightly
Products favored

10. Lets look at an example
Write a chemical equilibrium expression for the reaction
4HCl(g) + O2(g) ↔ 2Cl2(g) +2H2O(g)

11. Lets look at an example
At equilibrium, [HCl] = mol/L, and [H2]=[Cl2]=0.045 mol/L for the reaction H2(g) + Cl2(g) ↔ 2HCl(g). Find the value of Keq.

12. Review of Keq

13. Homework Continue to work on homework packet
Download and read Potassium-Iodide Clock lab
Come to class prepared for a quiz