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Calculating standard reaction enthalpy

Posted: Fri Jan 23, 2015 9:20 pm
by rachaeld_1D
Say we are given the equation 3Al(s)+3NH4ClO4(s)--> Al2O3(s)+AlCl3(s)+NO(g)+6H2O(g) and asked to calculate the standard delta H for the reaction. After looking up the enthalpies and summing the enthalpies for each product (multiplyie by the number of moles) and subtracting the sum of the reactants (multiplied by the number of moles for each product), why is the answer in units of kJxmol^-1? Since we multiplied by the number of moles for each product and reactant, shouldn't the answer just be in kJ?

Re: Calculating standard reaction enthalpy

Posted: Sat Jan 24, 2015 12:44 am
by Niharika Reddy 1D
I believe the "per mole" refers to the stoichiometric coefficients of the balanced reaction. So the delta H for that reaction would be ___kJ per 3 mol Al (s) for example, or per 1 mol NO (g).

Re: Calculating standard reaction enthalpy

Posted: Sat Jan 24, 2015 8:06 pm
by Justin Le 2I
After you solve for the delta H of that reaction, you will get your answer in kJ. You can then decide if you have to add a per mole to your answer depending on what the problem is asking.