1)

Question

MgO (s) + 2H (aq) -> Mg+2 (aq) + H2O (l)

2)
Mg+2 (aq) + H2 (g)-> Mg(s) + 2H+ (l)

3) equation 1+ equation 2 =

MgO (s) + H2 (g) -> Mg (s) + H2O (l)

is it correct?

if so, i need to write an expression which could be used to obtain the heat of formation of magnesium oxide (delta Hf MgO)

thanks

Answer 1

At first glance it looks OK except equation 1 should have + charge on the H^+.
But if you want to write an expression for delta Hf MgO, where is the oxygen?.
You want Mg + 1/2 O2 ==> MgO