posted by on .

For the equation:

deltaHrxn = qrxn / mol substance to calculate deltaH per mole

what does the mol substance mean? Does this mean that you use the mm of the substance or if you already calculated the # of moles of a substance do you use that?

It means you use the #moles of the substance you've already calculated.

ok thank you very much!!!

My qrxn value was 30267.23J and # of moles was 6.25e-3mol so that = 4842756.8 but are the units J/mol and do you think I should convert to kj?

If you used specific heat as 4.184 J/g*C then the units you have are J/mol. Most tests quote kJ/mol for this type of work.

The units for the specific heat of water that they gave me were J/ g x K

So in that case I would just divide my answer of4842756.8 by 1000 = 4842.76 kJ/mol correct?

yes.

I now need to find the enthalpies for Mg and MgO and then use the equations
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
MgO(s) + 2HCl(aq) ->MgCl2(aq) + H2O(l)
H2(g) + 1/2O2(l) delta H =-241.8 kJ

I do not understand how you find the values for the first two equations when there is only one value given.