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AE S2 K3: Le Chatelier’s Principle

CO 2 (g) CO 2 (aq). AE S2 K3: Le Chatelier’s Principle. The double arrow sign means that the forward reaction and reverse reaction are happening at the same time.

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AE S2 K3: Le Chatelier’s Principle

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  1. CO 2 (g)CO2(aq) AE S2 K3: Le Chatelier’s Principle The double arrow sign means that the forward reaction and reverse reaction are happening at the same time. All the time CO2 is going from the gaseous to aqueous phase AND at the same time the CO2 going from the aqueous to gaseous phase. This is an example of DYNAMIC EQUILIBRIUM At equilibrium both reactions are happening at the same rate and so the overall concentrations of CO2(g) and CO2(aq) NEVER change

  2. CO 2 (g)CO2(aq) AE S2 K3: Le Chatelier’s Principle If a bottle of soda is opened then the pressure of CO2(g) drops. This means that the equilibrium will shift to the left to make more gas thereby minimising the loss in pressure of CO2(g). This is observed when the bubbles of CO2 are produced in the drink as soon as the cap is opened.

  3. CO 2 (g)CO2(aq) AE S2 K3: Le Chatelier’s Principle What happens if the cap is screwed back on?

  4. CO 2 (g)CO2(aq) AE S2 K3: Le Chatelier’s Principle When the cap is screwed back on the pressure of CO2(g) increases rapidly as it cannot escape and the equilibrium is restored.

  5. AE S2 K3: Le Chatelier’s Principle Henri Louis Le Chatelier. Born 8/10/1850 Raised by his mother according to very rigorous and strict principles. Quote: ”All my life I maintained respect for law and order”

  6. AE S2 K3: Le Chatelier’s Principle States that: If a change is imposed on a closed system at equilibrium then the position of the equilibrium will shift to minimise that change.

  7. AE S2 K3: Le Chatelier’s Principle Another way of putting this is……

  8. AE S2 K3: Le Chatelier’s Principle The concentrations of reactants and products in a mixture at equilibrium will alter so as to counteract any change in concentration, temperature or gas pressure.

  9. AE S2 K3: Le Chatelier’s Principle Interestingly this principle can be applied to biology (homeostasis) and economics (price equilibrium)

  10. AE S2 K5: Describe, the solubility of carbon dioxide under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle.

  11. CO 2 (g)CO2(aq) AE S2 K5 :The Carbon Dioxide Equilibrium When we open a bottle of fizzy drink we lower the concentration CO 2 (g). The equilibrium shifts to the left to compensate for this change. In other words more aqueous CO2 turns to gaseous CO2 and we get lots of bubbles released.

  12. CO 2 (g)CO2(aq) The Carbon Dioxide Equilibrium +(heat) Dissolving a gas is an exothermic process. H = -ve So we can write Which helps us to predict the effect of opening a warm bottle of fizzy drink! Why do you think fizzy drinks are served cold?

  13. The Carbon Dioxide Equilibrium CO 2 (g)CO2(aq) + (heat) H = -ve Adding heat to an exothermic reaction makes it go in the endothermic direction (to take heat away). Taking heat away from an exothermic reaction makes it go in the exothermic direction (to replace the heat).

  14. The Carbon Dioxide Equilibrium CO 2 (g)CO2(aq) + (heat) H = -ve The CO2 equilibrium The forward reaction is …..othermic The back reaction is ..…othermic Increasing temperature increases the rate of the ……………… or …othermic reaction And we see …………… of gas coming out of ………..…. Decreasing temperature increases the rate of the ……………… or …thermic reaction And we see less bubles coming out of solution in ……… drinks.

  15. The Carbon Dioxide Equilibrium CO 2 (g)CO2(aq) + (heat) H = -ve The CO2 equilibrium The forward reaction is exothermic The back reaction is endothermic Increasing temperature increases the rate of the backward or endothermic reaction And we see bubbles of gas coming out of solution Increasing temperature increases the rate of the forwards or exothermic reaction And we see less bubble coming out of solution in colder drinks.

  16. The Carbon Dioxide Equilibrium In more detail

  17. CO 2 (g) + H2O (l)H2CO3(aq) H = -ve The Carbon Dioxide Equilibrium More often 1 + 2 are combined, written as: 1+2

  18. CO 2 (g) + H2O (l)H2CO3(aq) H = -ve H2CO3 (aq)HCO3-(aq) + H+ (aq) The Carbon Dioxide Equilibrium Then carbonic acid dissociates into a bicarbonate ion and a hydrogen ion (HCO3- and H+.) This is what makes it acidic. 1+2 3

  19. CO 2 (g) + H2O (l)H2CO3(aq) H = -ve H2CO3 (aq)HCO3-(aq) + H+ (aq) HCO3-(aq)CO3 2-(aq) + H+ (aq) The Carbon Dioxide Equilibrium Next the hydrogencarbonate ion dissociates into a carbonate ion and another proton. 1+2 3 4

  20. CO 2 (g) + H2O (l)H2CO3(aq) H = -ve H2CO3 (aq)HCO3-(aq) + H+ (aq) HCO3-(aq)CO3 2-(aq) + H+ (aq) The Carbon Dioxide Equilibrium Predict the affect of adding Na2CO3(aq) to soda! 1+2 3 4

  21. Now do some work…

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