Reversible Reactions

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Reversible Reactions

A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants 

(http://www.revisescience.co.uk/2011/images/reversible.jpg)(http://www.revisescience.co.uk/2011/images/ammonia.jpg)

  • If a reversible reaction takes place in a closed system, the state of equilibrium will always be reached
  • The reactions are taking place in both directions but the overall effect is nil because the forward and reverse reactions cancel out
  • REMEMBER: the reactions are taking place at exactly the same rate in both directions
  • Equilibrium --> the amounts of reactants and products will reach a certain balance and stay there
  • Closed System --> none of the reactants or products can escape
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Position of Equilibrium Depends on:

  • temperature
  • pressure
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Temperature

-all reactions are exothermic in one direction and endothermic in the other 

-if you raise the temperature, the endothermic reaction will increase to use up extra heat

-if you reduce the temperature, the exothermic reaction will increase and give out more heat

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Pressure

-many reactions have a greater volume on the one side, either of products or reactants

-raise the pressure --> encourage the reaction which produces less volume

-lower the pressure --> encourage the reaction which produces more volume

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Adding a catalyst

-DOES NOT CHANGE THE POSITION OF EQUILIBRIUM 

-catalysts speed up both the forward and reverse reactions by the same amount

-this means the reaction reaches equilibrium quicker, however you end up with the same amount of product as you would without a catalyst 

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