• Created by: DBaruch
  • Created on: 02-05-16 17:41

Dynamic equilibrium

  • Some Chemical reactions are reversible 
  • As reactants are used up the forward reaction slows down
  • The forward reaction will eventually go at the same rate as the backward reaction
  • It can only happen in a closed system which is at a constant temperature
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Le Chateliers principle

  • If you change the concentration, pressure or temperature of a reversible reaction you will change the position of the equilibrium
  • If the position moves to the left the backwards reaction is fastest
  • If the position moves to the right the fowards reaction is fastest
  • Le Chateliers principle tells you how the position of the equilibrium will change if the conditions change
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Using Le Chateliers principle

  • Changing Concentration: Increasing the concentration of a reactant will mean that the equilibrium will try to get rid of the extra reactant and does this by making more product. The equilibrium shifts to the right. Increasing the concentration of the product does the opposite of the reactant
  • Changing pressure: This only works with gases. Increasing pressure shifts the equilibrium to the side with fewer gas molecules and reduces the pressure. The opposite occurs when you decrease the pressure
  • Changing temperature: When you add heat the equilibrium moves in the endothermic direction to absorb this heat. Removing heat means that the equilibrium shifts in the exothermic direction to replace the heat. If the forward reaction is endothermic and reverse will be exothermic and vice versa
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The equilibrium constant

  • The equilibrium constant is the ratio worked out from the conentrations of the products and reactants after equilibrium is reached 
  • (http://www.chemguide.co.uk/physical/equilibria/definekc.gif)
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Factors affecting the equilibrium constant

  • Changing temperature: If the change means that more product is formed then the equilibrium constant will rise. If less product is formed then the equilibrium constant will decrease
  • Changing the concentration: The value of the equilibrium is constant so the equilibrium constant is fixed at a given temperature. So if the concentration of one thing in the equilibrium mixture changes then the concentrations of others must change to keep the value the same
  • Adding a catalyst: Catalysts have no effect on the any part of the equilibrium although the catalyst will increase the rate of both the forward and reverese reactions meaning that equilibrium will be reached faster
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