When to use Hess's Law

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Samantha Rundle 3K
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When to use Hess's Law

Postby Samantha Rundle 3K » Sun Jan 24, 2016 9:03 pm

When calculating enthalpy of a reaction, if the enthalpies of each compound are provided, I use the sum of the enthalpies of the products, minus those of the reactants, but in some cases, the enthalpy of each compound is provided, but Hess's Law must be used to calculate the enthalpy of the reaction and you have to write out the steps. If you are only given the enthalpy of each compound, how do you know when to use Hess's law, if the steps are not provided?

Thanks!

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Re: When to use Hess's Law

Postby Chem_Mod » Mon Jan 25, 2016 2:01 am

When the problem only gives you the enthalpies values without any reactions and asked to use Hess's Law, there's a great chance that it is enthalpy of formation. You can use its definition to write out the full reaction on your own.


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