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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: zmasterflex on November 24, 2011, 09:46:26 AM

Title: Enthalpy of MgCl2
Post by: zmasterflex 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

Title: Re: Enthalpy of MgCl2
Post by: Vidya 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