Chemistry

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Hi! I was studying for an exam (lol) and I came across something I don't quite understand.. could someone help me with Standard Enthalpy of Formation? The equation in my notes looks like this:
ΔHºrxn = ΣΔHºf(products) - ΣΔHºf(reactants)
Thanks in advance!

  • Chemistry -

    That is Hess' Law. IT states that the heat of reaction is equal to the sum of the heats of formations of the products minus the heats of formation of reactions.

    Example

    2HNO3 + Fe >> Fe(NO3)2 + H2 (g)

    The heat of reaction is equal to the heat of fromation of IronII nitrate-2*heatformation nitric acid. (the elments have zero Hf)

  • Chemistry -

    I think understand the concept but could you give me an example with numbers?

  • Chemistry -

    help please?

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