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chemical equilibrium

Discussion in 'DAT Discussions' started by BodybldgDoc, Apr 18, 2007.

  1. BodybldgDoc

    BodybldgDoc Guest

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    Jan 13, 2007
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    PCl5 + 4H20 ---> H3PO4 + 5HCl Delta H = -527KJ

    In the above reaction, if the temperature is increased, which direction would the reaction be shifted? To the left or to the right? and why?
     
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  3. twohearted

    twohearted The whistle go . . . 2+ Year Member

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    Oct 26, 2006
    I believe that since the rxn has a neg. delt. h, it would be considered exothermic. So heat could be written as a product: PCl5 +4H20 -> H3po4 + 5hcl + heat. L'chatliers principle states that when a perturbance in equilibrium occurs, the reaction will be shifted away from the perturbance (paraphrasing here.) Now if the heat would increase, I would think that the rxn would have to go left to resume equilibrium. Does that seem right?
     
  4. BodybldgDoc

    BodybldgDoc Guest

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    you are correct. thank you for the explanation.
     
  5. ATLATLATL

    ATLATLATL 2+ Year Member

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    Jan 9, 2007
    my question is...say for instance if the temperature increased or decreased then which way would it shift?
    and if it was endothermic...then?
     
  6. BodybldgDoc

    BodybldgDoc Guest

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    If it was endothermic, then the heat can be written as a reactant. so If you increase the heat from the side of the reactants it will shift towards the right i.e toward the products to bring the equation back to equilibrium.
     
  7. Lonely Sol

    Lonely Sol cowgoesmoo fan! 10+ Year Member

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    If temp. increases and endothermic = goes to right (forward)
    If temp. decreases and endothermic = goes to left

    If temp increase and exothermic = goes to left
    If temp decreases and exothermic = goes to right
     
  8. twohearted

    twohearted The whistle go . . . 2+ Year Member

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    Oct 26, 2006
    Lets generalize. Exothermic means Delta H < 0. Heat is a product so: Reactants -> Products + heat. This is the case for the example given. So if heat were added to the system, we must go to the left to restore equilibrium. This is intuitive because if the ratio of the products to reactants must be constant (equilibrium constant Keq), then it must follow that the addition of product would disturb the system such that the rxn would move to form more reactant so that the ratio remain the same(moves left.) Now then, if the heat in this exothermic system (Reactants -> Products + heat), were to be decreased, then naturally more product must be formed to keep that ratio constant (rxn goes right.) For an endothermic rxn we have: Reactants + Heat -> Products. So increasing the heat would drive the rxn to the right, so that the ratio is restored. Likewise lowering the heat in such a system would cause the reaction to move left. If I am completely wrong here, someone please correct me, but it seems pretty intuitive.
     
  9. Nasem

    Nasem 2+ Year Member

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    Aug 30, 2006
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    For endothermic:
    Reactants + head <-----> Product, H is +
    If you +T, shift right --->
    If you -T, shift left <---



    For exothermic:
    Reactants <-----> Product + heat, H is -
    If you +T, shift left <---
    If you -T, shift right --->
     

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