Note:
for
the reactions and DH values
H_{2}(g)
+ ½ O_{2}(g) ---> H_{2}O(l), DH_{f}°(H_{2}O)
= -286 kJ/mol
MgO(s) + 2 HCl(aq) ---> MgCl_{2}(aq) + H_{2}O(l),
DH(MgO) = (see above)
Mg(s) + 2 HCl(aq) ---> MgCl_{2}(aq) + H_{2}(g),
DH(Mg) = (see above)
Note:
The values of each of the factors a, b, and c in the below equation
are determined from the Hess' Law rules for combining the three
reactions that correspond to the three DH
values to produced the desired net reaction (Mg(s) + ½ O_{2}(g)
--->
MgO(s) ). An equation that is combined with no changes has a factor
of +1. An equation that is reversed before being combined has
a factor of -1. If all the coefficients of the reaction equation
are multiplied by a number, the factor is the same as that number. |