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- Le Châtelier's Principle - 1. When a chemical system is disturbed by a change in property the system adjusts in a way that opposes the change – an equilibrium.

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Presentation on theme: "- Le Châtelier's Principle - 1. When a chemical system is disturbed by a change in property the system adjusts in a way that opposes the change – an equilibrium."— Presentation transcript:

1 - Le Châtelier's Principle - 1

2 When a chemical system is disturbed by a change in property the system adjusts in a way that opposes the change – an equilibrium shift. What is an equilibrium shift? Equilibrium shift is the movement of a system at equilibrium resulting in a change in the concentration of reactants and products 2

3 According to Le Châtelier’s principle, an equilibrium shift always OPPOSES the change in the system 3

4  predicts that if more reactant or product is added to a system at equilibrium, then that system will undergo an equilibrium shift  increasing the concentration of reactant or product will cause the equilibrium to shift to consume some of the added reactant or product  decreasing the concentration of reactant or product will cause the equilibrium to shift to replace some of the removed reactant or product 4

5 Example: Freon-12 (chlorofluorocarbon) CCl 4(g) + 2 HF (g) CCl 2 F 2(g) + 2 HCl (g) 5 ⇋

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8  Energy in a chemical equilibrium equation can be treated as though it were a reactant or a product Endothermic Rxn: reactants + energy products Exothermic Rxn: reactants products + energy 8 ⇋ ⇋

9  energy can be added to or removed from a system by heating or cooling the container  equilibrium will shift to minimize change  increase in temperature the system shifts to consume some of the added thermal energy  decrease in temperature the system shifts to replace some of the removed thermal energy 9

10 Example: 2 SO 2(g) + O 2(g) 2 SO 3(g) + energy 10 ⇋

11  Boyle’s Law, the concentration of a gas in a container is directly related to the pressure of the gas (i.e. decreasing the volume to half its original value, doubles the concentration of every gas in the container)  always consider the total number of moles of gas reactants and the total number of moles of gas products Example: N 2(g) + 3 H 2(g) 2 NH 3(g) (1 mol + 3 mol) 4 mol 2 mol 11 ⇋

12  if the volume is increased (decrease in pressure) equilibrium shifts toward the side with the larger total amount of gaseous entities  if the volume is decreased (increase in pressure) equilibrium shifts towards the side with the smaller total amount of gaseous entities  system with equal number of gas molecules on each side of the equation will not shift after a change in volume  systems involving only liquids and solids are not affected appreciably – they are virtually incompressible – not affected by pressure 12

13 N 2(g) + 3 H 2(g) 2 NH 3(g) 13 ⇋

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15 Adding Catalysts  a catalyst decreases the time required to reach the equilibrium position, but does not affect the final position of equilibrium  lowers activation energy for both forward and reverse reactions by an equal amount – therefore occurs faster but equilibrium establishes in the same position as it would without the catalyst 15

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18 Adding Inert Gases  If a noble gas or a gas that cannot react with the entities in the system, the equilibrium position of the system will not change 18

19 The Reaction 19 MALE FEMALE

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27 Le Châtelier's Principle (worksheets) AND p. 457 Practice UC # 1, 2, 3, 4 and 5 27

28 StressChangeReason[CO 2(g) ][CO (g) ][O 2(g) ] Add CO 2(g) Remove CO 2(g) Add CO (g) 28 ⇋


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