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AS Chemistry endo and exo help

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    Hi there,

    I'm just getting a bit confused.

    If bond breaking is endothermic, and bond making is exothermic.

    Why is the definition of an endothermic reaction in my textbook:

    " A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants."

    Thanks for any help.
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    (Original post by IndyJK9)
    Hi there,

    I'm just getting a bit confused.

    If bond breaking is endothermic, and bond making is exothermic.

    Why is the definition of an endothermic reaction in my textbook:

    " A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants."

    Thanks for any help.
    As more energy was taken in to break the bonds in the reactants than was given out in making the bonds in the products. So the reactants are at a lower energy than the products.
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    (Original post by clownfish)
    As more energy was taken in to break the bonds in the reactants than was given out in making the bonds in the products. So the reactants are at a lower energy than the products.
    Thank you. I think I get it now. So it's about the level they're at rather than the enthalpy change?
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    (Original post by IndyJK9)
    Thank you. I think I get it now. So it's about the level they're at rather than the enthalpy change?
    Well both. If the reactants are at a lower energy level than the products, then the energy change (or enthalpy change) will be positive for the reaction, so therefore endothermic.

    Enthalpy change = energy of products-energy of reactants.

    Perhaps take a look at here, it might make it clearer http://www.knockhardy.org.uk/sci_htm_files/08enth.pdf
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    And I came here all excited about someone potentially asking about the diels-alder reaction
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    (Original post by illusionz)
    And I came here all excited about someone potentially asking about the diels-alder reaction
    They don't tend to cover it in AS chemistry
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    (Original post by clownfish)
    They don't tend to cover it in AS chemistry
    mmmm I realised
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    (Original post by illusionz)
    And I came here all excited about someone potentially asking about the diels-alder reaction
    Sorry to disappoint.

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Updated: May 22, 2012
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