I'm so baffled on how to work out the multiple choice questions on this topic... Can someone please explain a way.
Many thanks.
Consider the reactions
C2H4(g) + 2O2(g) → 2CO(g) + 2H2O(g) ∆H = −758 kJ mol−1
2C(s) + 2H2(g) → C2H4(g) ∆H = +52 kJ mol−1
H2(g) + O2(g) → H2O(g) ∆H = −242 kJ mol−1
The enthalpy of formation of carbon monoxide is
A −111 kJ mol−1
B −163 kJ mol−1
C −222 kJ mol−1
D -464 kJ mol−1
(The answer is A apparently)