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Le Chautelier's Principle

Le Châtelier’s Principle - equilibrium position changed when outside force disturbs the system

  • affected by concentration, temperature, pressure
  • change in reactant/product concentration >> reaction shifts to use up the added substance
  • lower volume, higher pressure >> reaction shifts to produce less moles of gas
  • higher volume, lower pressure >> reaction shifts to produce more moles of gas
  • higher temperature >> reaction shifts to use up extra energy (depends on whether reaction is exothermic/endothermic)
  • catalysts - only changes how fast equilibrium is achieved, not characteristics of equilibrium itself

Describe the effect on CaCO3(s) >> CaO(s) + CO2(g) when:  

  • pressure increased
    • shifts so that less gas is produced
    • shifts left
  • volume increased
    • same as decreasing the pressure
    • shifts right to produce more gas
  • adding CaCO3
    • no effect, it's a solid

For reaction PCl5(g) >> PCl3(g) + Cl2(g), K = 0.015 and DH = -375. What happens when Cl2 is removed?  

  • disregard K or DH
    • they have nothing to do w/ the problem
  • reaction shifts right to produce more Cl2

For endothermic equation N2(g) + O2(g) >> 2NO(g), K = 4.0 x 10-4. What happens when pressure is increased?  

  • again, disregard K
  • same amount of moles of gas on both sides of equation
  • reaction doesn't shift to either side

For endothermic equation N2(g) + O2(g) >> 2NO(g), K = 4.0 x 10-4. What happens when temperatre is increased?  

  • N2(g) + O2(g) + energy >> 2NO(g)
  • adding temperature >> adding energy
  • reaction shifts right to use up energy
Subject X2: 

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