Le chateliers principle


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  • From jaca 2:Add drops of lead (II) nitrate to a solution of sodium chloride until a precipitate forms. Divide into two test tubes. Put one test tube in ice water and one in hot water.Observe the change in precipitate
  • Jaca 2Prepare a mixture containing 2ml water and a small spatula tip of sodium chloride in a small beaker. Add 1-2 scoops of crystals of blue, hydrated copper (II) sulphate to this mixture. Stir to produce a slurry. Add crystals of sodium chloride to saturate the solution in chloride ions. Finally, add water slowly with stirring.
  • Le chateliers principle

    1. 1. Equilibrium
    2. 2. Reactions• Reactions involve reactants and products• Reactions that go to completion – Magnesium + oxygen → magnesium oxide • One way reaction, magnesium oxide cannot turn back into magnesium oxide• Reversible reactions – Have a forward and a reverse reaction – Carbon dioxide + water ↔ carbonic acid
    3. 3. Reversible reactions• The forward and reverse reactions occur at the same time, and never stop. – This means that it is a dynamic situation• At some point, the rate of the forward reaction is equal to the rate of the reverse reaction – This means that reactants are turning into products just as fast a products are turning back into reactants• At this point, the reaction is said to have reached EQUILIBRIUMAt equilibrium, the concentrations of the of the reactants andthe products are constant, but are not necessarily equal
    4. 4. Factors that disturb equilibrium• Change in temperature• Change in pressure• Change in concentration
    5. 5. Le Chatelier’s principle• Any change made to a reaction which is in equilibrium, will result in the equilibrium position moving to minimise the change made
    6. 6. Concentration• If the concentration of a reactant is increased, then the reaction will favour the forward reaction to reduce its concentration.• If the concentration of a reactant is decreased then the reaction will favour the reverse reaction to increase its concentration• A similar thing happens if you vary the concentration of the products• This “favouring” of a particular direction continues until the system returns to a point of equilibrium
    7. 7. Concentration continued• According to particle theory – An increase in concentration will provide more particles to be involved in the reaction
    8. 8. Pressure• Only affects reactions where there is at least one gas involved.• Increasing the pressure of a gas is similar to increasing its concentration, because the molecules of gas are pushed more closely together and are, therefore, involved in more reaction collisions.• That means the reaction will favour whichever direction decreases the amount of gas
    9. 9. Temperature• Reactions can be either exothermic (releases heat) or endothermic (absorbs heat). If a reaction is exothermic in one direction, it is endothermic in the other direction.• Using Le Chatelier’s principle with temperature: – An increase in temperature favours the endothermic reactions (the increase in temperature results in more energy being available to support the endothermic reaction) – A decrease in temperature favours the exothermic reaction
    10. 10. Experiment – effect of temperature on equilibrium
    11. 11. Experiment – Effect of concentration on equilibrium
    12. 12. Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process in terms of Le Chateliers principle.• The reaction between carbon dioxide and water is an example of an equilibrium reaction:• The forward reaction is exothermic (releases heat)
    13. 13. temperature• An increase in temperature will cause the reaction to go in the reverse direction – More carbon dioxide will be liberated – Hot soda loses its fizz faster• A decrease in temperature will cause the reaction to go in the forward direction – More carbonic acid will be formed
    14. 14. concentration• An increase in CO2 causes the reaction to move in the forward direction – Produces more carbonic acid• A decrease in CO2 causes the reaction to move in the reverse direction – Produces more CO2
    15. 15. pressure• An increase in pressure causes the reaction to move in the forward direction – That’s how they get the fizz in the drink in the first place• A decrease in pressure causes the reaction to move in the reverse direction – Thus, your drink is bubbly when you open it.
    16. 16. pH• As part of the forward reaction, the carbonic acid tends to dissociate in water, producing H+ ions and carbonate ions.• If we increased the acidity of our drink by adding citric acid – which also produces H+ ions, it would move the reaction in the reverse direction – Giving us more CO2 bubbles
    17. 17. Exercises• Complete the following questions from Conquering Chemistry 2 page 112 – 12 through to 16