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Topic: Enthalpy of MgCl2  (Read 7296 times)

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Offline zmasterflex

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Enthalpy of MgCl2
« on: November 24, 2011, 09:46:26 AM »
Greetings all. I had a lab from which I measured 6822.8 joules released by the reaction of Mg+2HCl->MgCl2+H2. The limiting reagent is Mg. I used 1.68E-2 moles (.0168 moles) of Mg meaning there is the same number of moles of MgCl2. Dividing 6822.8 Joules by .0168 to get joules per mole (and kj per mol) gives -406.1kj/mol.
Problem is is that apparently the heat of formation of MgCl2 is -641.8kj/mol.
Any suggestion as to where I went wrong? thanks

Offline Vidya

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Re: Enthalpy of MgCl2
« Reply #1 on: November 24, 2011, 09:58:43 AM »
here you have calculated the heat of the reaction
Mg+2HCl->MgCl2+H2.

however heat of formation is for Mg(s) + Cl2(g) ---> MgCl2(s)
there is a difference in the reactions

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