[Wsx594]

In a problem lab i'm to determine the heat of combustion for magnesium. The reaction is represented by Mg(s) + 1/2 O2 yields MgO(s). The accepted value is -601.8 Kj/mol. SpH of HCl is 4.184 J/g-k. I tested 2 reactions
1)  1g of MgO + 1M of 103.16 g of HCl which gave me a ΔT of 5.3 degrees C which I found q= -2309.77 J, I then found the molar enthalpy as -93.08 Kj/mol MgO 
2) .5 g Mg(s) + 1M of 102.3 g of HCl which gave me a ΔT of 21.7 degrees C which I used to find q= -9339.86 J, I then found the molar enthalpy as -453.91 Kj/mol Mg
Given these steps what would I do onward to find the heat of combustion?

[Borek]

Apply Hess law.

[Wsx594]

Ok so I applied hess's law and got the reactions:
MgCl2+ H2O(l) yields MgO + 2HCl which produces 93.08 Kj

Mg(s)+ 2HCl yields MgCl2+ H2 which produces -453.91 Kj

H2+1/2O2 yields H2O (l) which produces -142.9 Kj
 
when these are added together you get-557.73 Kj when the value should be -601.8 Kj
Is there any math i'm doing wrong? please help

[Borek]

At first sight logic looks OK. Not checking the numbers - 7% error is not that bad.

Energy unit is kJ, not Kj.