Calculating standard reaction enthalpy

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rachaeld_1D
Posts: 17
Joined: Fri Sep 26, 2014 2:02 pm

Calculating standard reaction enthalpy

Postby rachaeld_1D » Fri Jan 23, 2015 9:20 pm

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?

Niharika Reddy 1D
Posts: 127
Joined: Fri Sep 26, 2014 2:02 pm

Re: Calculating standard reaction enthalpy

Postby Niharika Reddy 1D » Sat Jan 24, 2015 12:44 am

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).

Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

Re: Calculating standard reaction enthalpy

Postby Justin Le 2I » Sat Jan 24, 2015 8:06 pm

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.


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