THE EQUILIBRIUM CONSTANT CHAPTER 18 PAGES 555-559 Chemistry

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

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

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?

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

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))

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

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

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

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

Lets look at an example At equilibrium, [HCl] = 0.0625 mol/L, and [H2]=[Cl2]=0.045 mol/L for the reaction H2(g) + Cl2(g) ↔ 2HCl(g). Find the value of Keq.

Review of Keq

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