# Combining enthalpies of formation and combustion in the context of Hess's law

I know that you can use enthalpy of combustion to work out formation, and Formation to work out enthalpy change. But can you use enthalpy of formation and combustion data is the same Hess's cycle to work out enthalpy change?

For example, we are trying to work out the enthalpy change for the reaction

$$\ce{A -> B}.$$

The alternative route is

$$\ce{A -> X -> B}.$$

We have been given combustion enthalpy data for $$\ce{A -> X}$$ and formation enthalpy data for $$\ce{X -> B}.$$

Could you work this out? Or does it always have to be the same type of enthalpy data in the alternative route?

• Hess's Law is path independent. Try Addition! – user55119 Mar 22 at 15:25
• Formation is from the elements. Combustion produces CO2 and H2O. So if you have the formation enthalpy of CO2 and H2O handy, you are all set. – Karsten Theis Mar 22 at 15:45