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    Hi,

    Can someone just summarize/breakdown Hess's Law or do you know a good website that explains it well? Enthalpy change of combustion and enthalpy of formation has also not been going well for me.

    Thanks
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    Hess's law states that the enthalpy change of a reaction is independent of the route taken to get from reactants to products.
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    the key terms "enthalpy change of combustion" and "enthalpy change of formation" are KEY to understanding hess.

    Standard enthalpy change of combustion - the enthalpy change associated with the complete combustion of one mole of fuel under standard conditions. In student speak - the energy released by the combustion of one mole of fuel.

    Standard enthalpy change of formation - the enthalpy change associated with the formation of one mole of compound from its elements in their standard states under standard conditions. In student speak - the energy required or released when one mole of a compound is made from the elements it is made from, those elements being in their standard states (H2(g), C(s), O2(g)).


    Any combustion reaction can be easily turned into a hess cycle. One side of the cycle is the combustion, the other two are the formations of the reactants and the products. The same is true of most reactions.

    In the case of this diagram, dH2=dH3-dH1
 
 
 
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