Warm Up Is combustion a reversible reaction? 2.Write the equilibrium constant for the reaction Fe 3 O 4 (s) + 4 H 2 (g) 3 Fe (s) + 4 H 2 O (g) 3.When a reversible reaction reaches equilibrium, the forward reaction rate is ______ as the reverse reaction rate Agenda -Turn in posters -Notes Unit 7-2 -Lab Equilibrium Homework Finish lab equilibrium

UNIT 7-2 LE CHATELIER’S PRINCIPLE

LE CHATELIER’S PRINCIPLE When system at equilibrium is disturbed, the system adjusts in a way to reduce the change and eliminate it (restoring balance) When system at equilibrium is disturbed, the system adjusts in a way to reduce the change and eliminate it (restoring balance)

All Stressed Out Stress is anything that causes a change in equilibrium that throws it off balance

Causes of Stress Changes in concentration –Adding or taking away the reactants or products will cause the system to shift

Causes of Stress Changes in Temperature –Depends on whether the forward reaction is endothermic or exothermic –Exothermic- heat is a product CaO + H 2 O  Ca(OH) 2 + HEAT –Endothermic- heat is a reactant 2Fe 2 O 3 + 3C + HEAT  4Fe + 3CO 2 Which direction will it shift if heat is added?

Causes of Stress Changes in Pressure –Not a cause of stress for reactions in solutions –Only gases are affected Example: N 2(g) + 3H 2(g) ⇌ 2NH 3(g) 4 moles ⇌ 2 moles Increase Pressure Decrease Pressure

Causes of Stress Changes in Pressure – Increases in pressure will shift the reaction to the side with less total molecules –Decreases in pressure will shift reactions to the side with more total molecules

Check for Understanding 2H 2 (g) + O 2 (g) 2H 2 O (g) 1.Which way will it shift if you add H 2 to the system? 2.Which way will it shift if you decrease H 2 O? 3.Which way will it shift if you decrease the pressure? 4.Which way will it shift if you decrease temperature?

Lab Equilibrium/Paper Folding 1.Each group will need to cut out about squares (1x1 inch) 2.Person #1 fold the paper so that the shaded side is showing 3.Person #2 fold the paper so that the unshaded side is showing 4.DO NOT RESTART after 30 seconds, just keep folding 5.Stop every 30 seconds to count your pieces of paper

Assignments -Notes Summary -Lab equilibrium