Le Chateliers Principle and Equilibrium Chemistry Mrs Coyle
Le Chatelier’s Principle and Equilibrium Chemistry Mrs. Coyle
Reversible Reactions Ø Occur simultaneously in both directions.
Example of a Reversible Reaction Ø Heat +N 2 O 4 Colder temp (g) 2 NO 2 (g) Warmer temp http: //genchem. wisc. edu/demonstrations/Images/13 equil/NO 2 N 2 O 4. jpg
Equilibrium Ø A state of balance at which the rates of the forward and reverse reactions are equal.
Equilibrium Position Ø The relative concentrations of reactants and products at equilibrium. Ø At this point the concentrations don’t change unless a stress is applied to change the equilibrium.
Le Châtelier’s Principle Ø If a stress is applied to a system in dynamic equilibrium, the system changes to relieve the stress. Ø System stresses: l l l Concentration of reactants or products Temperature Pressure
Effect of Concentration of Reactants Ø Adding reactant shifts the reaction toward the products. Why? Ø Stress: Increasing reactants Ø Relief: Decreasing reactants Ø Shift: to the right (products) H 2 O (l) + CO 2 (g) H 2 CO 3 (aq)
Effect of Concentration of Products Ø Adding products shifts the reaction toward the reactants. Why? Ø Stress: Increasing products Ø Relief: Decreasing products Ø Shift: to the left (reactants) H 2 O (l) + CO 2 (g) H 2 CO 3 (aq)
Effect of Temperature Ø Increasing the temperature causes the equilibrium to shift in the direction that absorbs heat. Stress: Increase in Temp Ø Relief: Decrease in Temp Ø Shift: Towards the left SO 2 (g) + O 2 (g) 2 SO 3 (g) + heat
Effect of Pressure Ø Affects gases only. Ø For unequal number of moles of reactants and products, if pressure is increased, the equilibrium will shift to reduce the number of particles. Ø For equal number of moles of reactants and products, no shift occurs. 2 NO 2 (g) N 2 O 4 (g)
Ex: Effect of Pressure 2 NO 2 (g) N 2 O 4 (g) Stress: increasing the pressure Relief: decreasing the pressure Shift: to the right (side of less molecules)
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