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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
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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 H2 CH4 + H2O • 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 H2 CH4 + H2O H2 + I2 2 HI
4. Changes in Temperature • Heat acts as a product or a reactant in an equation. • Best understood in the example: CO + 3 H2 CH4 + H2O DH = -206.5 kJ DH 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
Pop Quiz: 1. Use Le Chatelier’s principle to predict how each of these changes would affect the following equilibrium system: N2 + 3 H2 2 NH3 • Removing hydrogen from the system • Adding ammonia to the system • Adding hydrogen to the system 2. How would decreasing the volume of the reaction vessel affect each of these equilibria? • 2 SO2 (g) + O2 (g) 2 SO3 (g) • H2 (g) + Cl2 (g) 2 HCl (g) • 2 NOBr (g) 2 NO (g) + Br2 (g)
3. In the following equilibrium, would you raise or lower the temperature to obtain these results? C2H2 (g) + H2O (g) CH3CHO (g) + heat a. an increase in the amount of CH3CHO b. a decrease in the amount of C2H2 c. an increase in the amount of H2O