Equilibrium Notes: Factors Affecting Equilibrium Part 2

1. Le Chatelier’s Principle There are ways to control equilibria Principle: if a stress is applied to a system at equilibrium, the system will shift in the direction that relieves the stress Stress = any kind of change that upsets the equilibrium

2. Changes in Concentration CO + 3 H 2 CH 4 + H 2 O Increase a reactant = causes a shift to the right to make more product Increase in product = causes shift to the left to make more reactant Decrease reactant = causes shift to left to make more reactant Decrease product = causes shift to right to make more product

3. Changes in Volume/Pressure Changing the volume of the reaction vessel can alter the equilibrium By decreasing volume you increase pressure. To relieve the stress of increased pressure, the rxn will shift toward decreasing the amount of moles. Only happens if there is a difference between the amount of moles of reactants and products. CO + 3 H 2 CH 4 + H 2 O H 2 + I 2 2 HI

4. Changes in Temperature Heat acts as a product or a reactant in an equation. Best understood in the example: CO + 3 H 2 CH 4 + H 2 O  H = kJ  H is negative so forward direction is exothermic and heat is a product. Add heat (increase temperature) = shift to the left Remove heat (decrease temperature) = shift to right

Practice: 1.Use Le Chatelier’s principle to predict how each of these changes would affect the following equilibrium system: N H 2 2 NH 3 a.Removing hydrogen from the system b.Adding ammonia to the system c.Adding hydrogen to the system 2.How would decreasing the volume of the reaction vessel affect each of these equilibria? a.2 SO 2 (g) + O 2 (g) 2 SO 3 (g) b.H 2 (g) + Cl 2 (g) 2 HCl (g) c.2 NOBr (g) 2 NO (g) + Br 2 (g)

3. In the following equilibrium, would you raise or lower the temperature to obtain these results? C 2 H 2 (g) + H 2 O (g) CH 3 CHO (g) + heat a. an increase in the amount of CH 3 CHO b. a decrease in the amount of C 2 H 2 c. an increase in the amount of H 2 O