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EQUILIBRIUM 2

EQUILIBRIUM 2. REACTION YIELDS  . Equilibrium. Very few reactions proceed unhindered to completion. Some begin reversing as soon as products are present. Examples of reversible reactions Melting ice block H 2 O (s) H 2 O (l) Ni-Cad rechargeable batteries . Equilibrium.

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EQUILIBRIUM 2

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  1. EQUILIBRIUM 2 • REACTION YIELDS  

  2. Equilibrium • Very few reactions proceed unhindered to completion. • Some begin reversing as soon as products are present. • Examples of reversible reactions • Melting ice block • H2O (s) H2O (l) • Ni-Cad rechargeable batteries 

  3. Equilibrium • Chemical reactions that consist of two opposing processes (forward and reverse reactions) will eventually reach an equilibrium. • The state of equilibrium is characterized by the forward and reverse reactions proceeding at the same rate • i.e. reactions do not stop ‑ we have a dynamic situation

  4. Dynamic Equilibrium • Characterized by the following criteria • amounts and concentrations of substances remain constant • total gas pressure remains constant • temperature remains constant • the reaction is incomplete (all substances involved in the reaction are present)

  5. Equilibrium N2 + 3H2 2NH3 rate 2NH3 N2 + 3H2 time Equilibrium first established Variation of the rates of the forward and reverse reactions with time

  6. The Equilibrium Law • For the general equilibriumxA + yB pC + qD • It can be stated = constant = K [C]p [D] q [A]x [B]y

  7. Equilibrium Law • K allows for the evaluation of the concentration fraction at any time. • When the system is at equilibrium the concentration fraction is constant ‑ so called the equilibrium constant (K). • For a particular reaction, K is constant for all equilibrium mixtures (provided temperature remains constant)

  8. Information From The Equilibrium Constant • If K is about 104 to 10–4 there will be significant amounts of both reactants and products present at equilibrium • If K is very large (> 104) the equilibrium mixture consists mostly of products • If K is very small (< 10–4 ) the equilibrium mixture consists mostly of reactants

  9. Le Chatelier's Principle  • Whenever a change is made to a system at equilibrium, the equilibrium position will shift to partially oppose the change 

  10. Disturbing Equilibrium • There are 4 major means of disturbing a system at equilibrium • Adding or removing a reactant or product • Changing the pressure by changing the volume (gases only) • Dilution (for solutions only) • Changing the temperature

  11. Disturbing Equilibrium • Addition of a catalyst will increase both the rate of the forward and reverse reactions equally • It will simply reduced the time taken to reach equilibrium.

  12. Effect of Temperature on Equilibria • As temperature INCREASES • For exothermic reactions, value of K decreases and amounts of products decrease • For endothermic reactions, value of K increases and amounts of products increase

  13. Effect of Temperature on Equilibria • The value of K depends on temperature • When stating a value of K, the temperature at which the constant was calculated must also be stated • Temperature is the only change that can be made to a system at equilibrium that will actually change the equilibrium constant (ie K is temperature dependant)

  14. Consider the Reaction • N2(g) + 3H2(g) 2NH3(g)

  15. Effect on Equilibrium of Adding / Removing Reactant or Product • N2(g) + 3H2(g) 2NH3(g)

  16. Effect of Adding Nitrogen • Causes the rate of the forward reaction to increase • More ammonia is formed [NH3] increases • This causes the rate of the back reaction to increase to re form more N2 and H2

  17. Effect of Adding Nitrogen [N2] concentration [H2] [NH3] time Initial equilibrium

  18. Effect of Adding Nitrogen [N2] concentration [H2] [NH3] time Initial equilibrium Nitrogen added

  19. Effect of Adding Nitrogen [N2] concentration [H2] [NH3] System returns to equilibrium time Initial equilibrium Nitrogen added

  20. Effect of Adding Nitrogen [N2] concentration [H2] [NH3] System returns to equilibrium time Initial equilibrium Nitrogen added New equilibrium established

  21. Effect of Adding Hydrogen [N2] concentration [H2] [NH3] time Hydrogen added Initial equilibrium

  22. Effect of Adding Hydrogen [N2] concentration [H2] [NH3] time Hydrogen added Initial equilibrium

  23. Effect of Adding Hydrogen [N2] concentration [H2] [NH3] System returns to equilibrium time Hydrogen added Initial equilibrium

  24. Effect of Adding Hydrogen [N2] concentration [H2] [NH3] System returns to equilibrium time Hydrogen added Initial equilibrium New equilibrium established

  25. Effect of Adding Product • Leads to Formation of more Reactants • A nett back reaction occurs

  26. Effect of Adding Ammonia [N2] concentration [H2] [NH3] time Initial equilibrium

  27. Effect of Adding Ammonia [N2] concentration [H2] [NH3] time Ammonia added Initial equilibrium

  28. Effect of Adding Ammonia [N2] concentration [H2] [NH3] System returns to equilibrium time Ammonia added Initial equilibrium

  29. Effect of Adding Ammonia [N2] concentration [H2] [NH3] System returns to equilibrium time Ammonia added Initial equilibrium New equilibrium established

  30. Effect of Changing Reactant / Product • Addition of Reactant leads to more Products being formed (Nett Forward Reaction) • Addition of Product leads to more Reactants being formed (Nett Back Reaction) • Removal of Reactant leads to less Products being formed (Nett Back Reaction) • Removal of Product leads to less Reactants being formed (Nett Forward Reaction)

  31. Changing Pressure • Pressure can be changed by increasing or decreasing the volume of the container while keeping the temperature constant. • Need to examine 2 examples

  32. Changing Pressure • 2SO2(g) + O2(g) 2SO3(g) • 3 gas particles 2 gas particles • A nett forward reaction • involves a reduction in the number of gas particles, • so a reduction in pressure • A nett back reaction • Involves an increase in the number of gas particles • So an increase in pressure

  33. Changing Pressure • 2SO2(g) + O2(g) 2SO3(g) • 3 gas particles 2 gas particles • Using Le Chatelier’s Principle • An increase in pressure will lead to • Be adjusted by a reduction in pressure • A nett forward reaction will occur increasing the amount of sulphur trioxide present at equilibrium

  34. Changing Pressure • 2SO2(g) + O2(g) 2SO3(g) SO2 5 O2 3 SO3 1 TOTAL 9

  35. Changing Pressure • 2SO2(g) + O2(g) 2SO3(g) Nett forward reaction Increased pressure SO2 1 O2 1 SO3 5 TOTAL 7

  36. Changing Pressure • N2O4(g) 2NO2(g) • 1 gas particles 2 gas particles • Colourless Brown • A nett forward reaction • involves an increase in the number of gas particles, • so an increase in pressure • A nett back reaction • Involves a decrease in the number of gas particles • So a decrease in pressure

  37. Changing Pressure • N2O4(g) 2NO2(g) • An equilibrium mixture of the gases was compressed • Initially darkened - [NO2] increases • Then colour of gas mixture fades • Nett backward reaction

  38. Changing Pressure • N2O4(g) 2NO2(g) [N2O4] concentration [NO2] time Initial equilibrium

  39. Changing Pressure • N2O4(g) 2NO2(g) [N2O4] concentration [NO2] time Initial equilibrium Increase of pressure

  40. Changing Pressure • N2O4(g) 2NO2(g) [N2O4] concentration [NO2] time Initial equilibrium Increase of pressure System returns to equilibrium

  41. Changing Pressure • N2O4(g) 2NO2(g) [N2O4] concentration [NO2] time Initial equilibrium Increase of pressure System returns to equilibrium New equilibrium established

  42. Adding an inert gas • Total pressure of equilibrium system can be changed without changing the volume of the container by adding an inert gas • There is no increase in concentrations of reactants or products • No change in equilibrium

  43. Dilution • When dilution occurs, a net reaction results which produces the greater number of particles • The effect of diluting the solution by adding water is • A net reaction in the direction that produces more particles

  44. Dilution • Fe3+(aq) + SCN–(aq) Fe(SCN)2+(aq) • 2 particles in soln 1 particle in soln • Dilution of this equilibrium will result in a nett back reaction • Results in an increase of [Fe3+] and [SCN–]

  45. Change in Temperature • Using Le Chatelier’s Principle • Exothermic reaction can be written as • Reactants Products + energy • Heating increases the energy of the substances • Principle says the reaction will oppose an increase in energy by removing energy • A nett back reaction occurs • Less product and more reactants now present

  46. Change in TemperatureExothermic A + B C + D [D] concentration [C] [B] [A] time Initial equilibrium

  47. Change in TemperatureExothermic A + B C + D [D] Temperature increases concentration [C] [B] [A] time System returns to equilibrium Initial equilibrium Temperature increases

  48. Change in TemperatureExothermic A + B C + D [D] Temperature increases concentration [C] [B] [A] time System returns to equilibrium Initial equilibrium Temperature increases New equilibrium established

  49. Change in TemperatureEndothermic A + B C + D [D] concentration [C] [B] [A] time Initial equilibrium

  50. Change in TemperatureEndothermic A + B C + D [D] Temperature increases concentration [C] [B] [A] time System returns to equilibrium Initial equilibrium Temperature increases

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