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Le Châtelier’s principle. The significance of Kc values If Kc is small (0.001 or lower), [products] must be small, thus forward reaction is weak If Kc.

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Presentation on theme: "Le Châtelier’s principle. The significance of Kc values If Kc is small (0.001 or lower), [products] must be small, thus forward reaction is weak If Kc."— Presentation transcript:

1 Le Châtelier’s principle

2 The significance of Kc values If Kc is small (0.001 or lower), [products] must be small, thus forward reaction is weak If Kc is large (1000 or more), [products] must be large, thus forward reaction is strong [Products] Kc = [Reactants] Reactants  Products If Kc is about 1, then reactants and products are about equal but not exactly since they may be raise to different exponents

3 Stresses to equilibria Changes in reactant or product concentrations is one type of “stress” on an equilibrium Other stresses are temperature, and pressure.

4 The response of equilibria to these stresses is explained by Le Chatelier’s principle: If an equilibrium in a system is upset, the system will tend to react in a direction that will reestablish equilibrium Thus we have: 1) Equilibrium, 2) Disturbance of equilibrium, 3) Shift to restore equilibrium Le Chatelier’s principle predicts how an equilibrium will shift (

5 N 2 + 3H 2  2NH kJ Summary of Le Chatelier’s principle E.g. N 2 + 3H 2  2 NH kJ Pressure (due to decreased volume): increase in pressure favors side with fewer molecules Amounts of products and reactants: equilibrium shifts to compensate  N 2  H 2 Temperature: equilibrium shifts to compensate:  Heat shift right shift left

6 Part 1: changes in reactant or product concentrations Cu NH 3 Cu(NH 3 ) H 2 O Ni NH 3 Ni(NH 3 ) H 2 O NH 3 + H + (NH4)

7 Part A: copper and nickel ions Do not do Nickel ions Question 4 the answer is pale green Question 5 the answer is Violet Question 6 the answer is pale green

8 Part B: Cobalt ions Do not do Co Cl - CoCl H 2 O Question 8 the answer is pale pink Question 9 the answer is deep blue Question 10 the answer is pale pink

9 Part II. Equilibria involving sparingly soluble salts Ag + + CO 3 -2 Ag 2 CO H + + CO 3 -2 H 2 O + CO 2

10 Part II. Equilibria involving sparingly soluble salts Ag + + Cl - AgCl Ag + + 2NH 3 Ag(NH 3 ) 2 + heat NH 3 + H + (NH4)

11 Part III. Temp on Equilibria Heat + CoCl 2 + 6H 2 O Co(H 2 O) 6 + 4Cl


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