Hess's Law? Pleeeease help!! Calculate enthalpy change for the reaction?

Question

2C8H18(l)+ 21 O2(g) --> 8CO(g) + 8CO2(g) + 18H2O
???delta H

Given
2C8H18(l) + 25 O2(g) ---> 16CO2 (g) + 18 H2O(l)
delta H -11,020 kJ

2CO (g) + O2 (g) --> 2CO2(g) delta H -566.0 kJ

Answer 1

Given:
2C8H18 + 25 O2 ---> 16CO2 + 18 H2O...(1)
delta H -11,020 kJ
2CO + O2 ---> 2CO2...(2)
delta H -566.0 kJ
(1) -4*(2):
2C8H18(l)+ 21 O2(g) --> 8CO(g) + 8CO2(g) + 18H2O
delta H = -11,020 kJ + 4*566.0 kJ = -8756 kJ.