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Scholar
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Date Posted: 7/24/2008 7:55:24 AM  Status: Live
hess law help extra cred due in 1 hours
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Question Details:
Calculate the standard enthalpy of formation (delta H f) of ethanol C2H5OH from the heat of combustion of ethanol, which is -1368 kJ/mol by using tabulated standard enthalpies of formation for CO2 and H2O.


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Sage
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Date Posted: 7/24/2008 11:02:19 PM  Status: Live
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Response:
the combustion reaction of ethanol is
            C2H5OH(l) + 3O2(g) -----> 2CO2(g) + 3H2O(l)
the standard enthalpy change for the reaction can be calculated as
ΔH0rxn = [2ΔH0f(CO2(g)) + 3ΔH0f(H2O(l)) ]-[1ΔH0f(C2H5OH(l))+3ΔH0f(O2(g)) ]
-1368KJ/mol = [2(-393.5)+3(-285.8)]-[1ΔH0f(C2H5OH(l))+3(0)]
ΔH0f(C2H5OH(l)) = -276.4KJ/mol



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