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.
In the equation ΔHrxn = qrxn / mol substance, the term "mol substance" refers to the number of moles of the substance involved in the reaction.
To calculate ΔH per mole, you need to know the amount of substance in moles, rather than the molecular mass (mm) of the substance. If you already have the number of moles of the substance, you can use that directly in the equation.
If you have the mass of the substance instead of the number of moles, you can convert it to moles using the substance's molar mass. The molar mass is the mass of one mole of the substance and is given in units of grams per mole (g/mol). You can use the equation:
moles = mass / molar mass
Once you have the number of moles, you can substitute it into the equation ΔHrxn = qrxn / mol substance to calculate the ΔH per mole.