enthalpy chemistry help!!!?

Question

2 Mg(s) + O2(g) 2 MgO(s) ∆H = -1204 kJ

(a) How many grams of MgO are produced during an enthalpy change of 96.0 kJ?

(b) How many kilojoules of heat are absorbed when 7.80 g of MgO(s) are decomposed into Mg(s) and O2(g) at constant pressure?

Answer 1

a)
2Mg+02(g)= 2MgO(s)
2 moles of Mg weighs around 2* 24.305 grams because the atomic weight of Mg=24.305Atomic Units(you don't need that pesky avocado's number) 2 moles of O weighs 15.9994 grams.
So once we convert moles to grams
2 moles MgO(s)=48.61g+31.9988g=80.6088gMgO(s)
H=-1204kJ so if change in
H=-96kJ then you are using about 96kJ/1204kJ=.079734193

so 80.6088gMgO(s)*.079734193=6.427277617 or rounded to 4 decimal places
6.4273g.

b)7.80g/80.6088g=.0967636288, *1204kJ = 116.5034091kJ or rounded to 4 decimal places 116.5034