How do I know which enthelpy change to calculate?

[Physicsman788]

How do I know if I need to find the enthalpy of combustion or the enthalpy of formation? I know the equation to find the enthalpy change of each them but I don't know on a question if I have to find the enthalpy of combustion or the enthalpy of formation.

 

[Borek]

It must depend on the question, there is no "one size fits all" answer.

 

[Lord Jestocost]

The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one mole of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.

https://www.chemguide.co.uk/physical/energetics/definitions.html