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Equilibrium Systems

Equilibrium Systems. 15.2: Le Châtelier’s Principle. Le Châtelier’s Principle. can predict how certain changes in a reaction will affect the position of equilibrium

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Equilibrium Systems

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  1. Equilibrium Systems 15.2: Le Châtelier’s Principle

  2. Le Châtelier’s Principle • can predict how certain changes in a reaction will affect the position of equilibrium • when a chemical system at equil. is disturbed by a change in the system, the system will react in a direction opposing the change until a new equil. is reached

  3. Le Châtelier’s Principle con’t • he described a 3 stage process • Initial equilibrium • Shifting non-equilibrium • New equilibrium • Catalysts can be used to decrease the time to reach the new equil. position • does not affect the final position of that equilibrium

  4. Changing Concentration • system will shift away from the added component or towards a removed component • a change in conc. of a pure solid or liquid does not cause an equil. shift • Ex: N2 + 3H2 2NH3 • if more N2 is added, then equilibrium position shifts to the right • if some NH3 is removed, then equilibrium position shifts to the right

  5. Change in Pressure • adding or removing gaseous reactant or product is same as changing conc. • adding inert or uninvolved gas • increase the total pressure • doesn’t effect the equilibrium position

  6. Change in Pressure • changing the volume • decrease V • decrease in # gas molecules • shifts towards the side of the reaction with less gas molecules • increase V • increase in # of gas molecules • shifts towards the side of the reaction with more gas molecules

  7. Change in Temperature • all other changes alter the concentration at equilibrium position but don’t actually change value of K • value of K does change with temperature

  8. Change in Temperature • if energy is added, the reaction will shift in direction that consumes energy • treat energy as a: • reactant: for endothermic reactions • product: for exothermic reactions

  9. As4O6(s) + 6C(s) ⇄ As4(g) + 6CO(g) • add CO • to left • add C • no shift • remove C • no shift • add As4O6 • no shift • remove As4O6 • no shift • remove As4 • to right • decrease volume • to left • add Ne gas • no shift

  10. P4(s) + 6Cl2(g) ⇄ 4PCl3(l) • decrease volume • to right • increase volume • to left • add P4 • no shift • remove Cl2 • to left • add Kr gas • no shift • add PCl3 • no shift

  11. energy + N2(g) + O2(g) ⇄ 2NO(g) • endo or exo? • endothermic • increase temp • to right • increase volume • no shift • decrease temp • to left

  12. Homework • Textbook p695 #1-3, LSM 15.2J • LSM summary 15.2C,D,F

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