Calculate H for the process Zns Ss 2O g ZnSO s 298 24 from

Calculate H°   for the process Zn(s) + S(s) + 2O (g) ZnSO (s) 298 24
from the following information:
Zn(s) + S(s) ZnS(s)   H°   = 206.0 kJ 298
ZnS(s) + 2O (g) ZnSO (s)   H°   = 776.8 kJ

Solution

1) Zn + S ---> ZnS , ,,, dH1 = -260 kJ

2) ZnS + 2 O ---> ZnSO ,,,,, dH2 = -776.8 kJ

3) Zn + S + 2 O ---> ZnSO ,,,,,, dH3 = ???

it can be derived that

equation 3 = equation 1 + equation 2

now according to Hess`s law

dH3 = dH1 + dH2

dH3 = -206 kJ + (-776.8 kJ)

dH3 = -982.8 kJ

so

the required dHo value is -982.8 kJ