Le châtelier’s principle

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Le châtelier’s principle

  1. 1. Le Châtelier’s Principle<br />System starts at equilibrium.<br />A change/stress is then made to system at equilibrium.<br />Change in concentration<br />Change in volume<br />Change in pressure<br />Change in Temperature<br />Add Catalyst<br />System responds by shifting to reactant or product side to restore equilibrium.<br />
  2. 2. N2 (g) + 3H2 (g) 2NH3(g)<br />Equilibrium shifts left to offset stress<br />Add<br />NH3<br />Le Châtelier’s Principle<br />If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position. <br /><ul><li> Changes in Concentration</li></ul>14.5<br />
  3. 3. Remove<br />Remove<br />Add<br />Add<br />aA + bBcC + dD<br />Le Châtelier’s Principle<br /><ul><li> Changes in Concentration continued</li></ul>Change<br />Shifts the Equilibrium<br />Increase concentration of product(s)<br />left<br />Decrease concentration of product(s)<br />right<br />Increase concentration of reactant(s)<br />right<br />Decrease concentration of reactant(s)<br />left<br />14.5<br />
  4. 4. A (g) + B (g) C (g)<br />Le Châtelier’s Principle<br /><ul><li> Changes in Volume and Pressure</li></ul>(Only a factor with gases)<br />Change<br />Shifts the Equilibrium<br />Increase pressure <br />Side with fewest moles of gas<br />Decrease pressure<br />Side with most moles of gas<br />Increase volume<br />Side with most moles of gas<br />Decrease volume<br />Side with fewest moles of gas<br />14.5<br />
  5. 5. Le Chatelier’s Principle<br /><ul><li>Temperature – increasing the temperature causes the equilibrium position to shift in the direction that absorbs heat
  6. 6. If heat is one of the products (just like a chemical), it is part of the equilibrium
  7. 7. so cooling an exothermic reaction will produce more product, and heating it would shift the reaction to the reactant side of the equilibrium: C + O2(g)-> CO2(g) + 393.5 kJ</li></li></ul><li>Change<br />Exothermic Rx<br />Endothermic Rx<br />Increase temperature <br />K decreases<br />K increases<br />Decrease temperature<br />K increases<br />K decreases<br />Le Châtelier’s Principle<br /><ul><li>Changes in Temperature
  8. 8. Only factor that can change value of K</li></ul>14.5<br />
  9. 9. Le Châtelier’s Principle<br /><ul><li> Adding a Catalyst
  10. 10. does not change K
  11. 11. does not shift the position of an equilibrium system
  12. 12. system will reach equilibrium sooner</li></li></ul><li>uncatalyzed<br />catalyzed<br />Catalyst lowers Ea for both forward and reverse reactions.<br />Catalyst does not change equilibrium constant or shift equilibrium.<br />14.5<br />
  13. 13. Change Equilibrium<br /> Constant<br />Le Châtelier’s Principle<br />Change<br />Shift Equilibrium<br />Concentration<br />yes<br />no<br />Pressure<br />yes<br />no<br />Volume<br />yes<br />no<br />Temperature<br />yes<br />yes<br />Catalyst<br />no<br />no<br />14.5<br />

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