Chemical Equilibrium

1. Chemical Equilibrium Dr. Walker

2. What will you learn? • Reactions can occur in two directions simultaneously. • LeChatelier’s Principle indicates which way the reaction will shift with a change in temperature, pressure, or concentration.

3. Reversible Reactions • Defined • A chemical reaction in which the products can react to re-form the reactants • Usually represented by a double sided arrow • Equilibrium can be to the left or the right depending on conditions 2 HgO(s)  2Hg(l) + O2(g)

4. Dynamic Equilibrium • Reactions continue to take place • Reactant molecules continue to be converted to product (forward reaction) • Product continues to be converted to reactant (reverse reaction) • Forward and reverse reactions take place at the same rate at equilibrium Reactants become products 2 HgO(s)  2Hg(l) + O2(g) Products become Reactants

5. Write all Chemical Equilibrium • When forward and reverse reactions take place at the same rate • No overall change in the actual amount present in the reaction • Does not imply equal concentrations of reactants and products, only constant concentrations

6. Write all

7. Write bold Le Chatelier’s Principle • “If a stress is applied to a system in dynamic equilibrium, the system changes to relieve the stress.” • Chemical reactions try to balance out what they perceive to be normal. • Stresses that upset the equilibrium of a chemical system • Concentrations of reactants and products • Temperature • Pressure

8. Write bold Concentration and Le Chatelier’s Principle • Changes in concentration disturb the equilibrium, so the system adapts to minimize the effects of the disturbance • System changes to use up the “excess” reactant • If you add something to one side, the equilibrium moves in the opposite direction

9. An Example

10. An Example

11. Temperature and LeChatelier • Exothermic Reaction • Energy is a product • Increase Temperature: Favors Reactants • Endothermic Reaction • Energy is a reactant • Increase Temperature: Favors Product

12. LeChatelier Example #1 A closed container of ice and water is at equilibrium. Then, the temperature is raised. Ice + Energy  Water right The system temporarily shifts to the _______ to restore equilibrium.

13. LeChatelier Example #2 A closed container of N2O4 and NO2 is at equilibrium. NO2 is added to the container. N2O4 (g) + Energy  2 NO2 (g) left The system temporarily shifts to the _______ to restore equilibrium.

14. LeChatelier Example #3 A closed container of water and its vapor is at equilibrium. Vapor is removed from the system. water + Energy  vapor right The system temporarily shifts to the _______ to restore equilibrium.

15. A Real World Example

16. A Real World Example

17. Write bold Pressure and LeChatelier • 3 H2(g) + N2(g) 2 NH3(g) • As pressure increases, the number of moles of product increases • Think of it as adding to the side with more moles • Shifts towards side with fewer moles • Particles are forced to come closer together, therefore reacting the reactants to form more products

19. Answer!