# Standard heat of reaction

1. ### Maylis

790
Hello,

I am confused about the following scenario.

Suppose I have the reaction

CO (g) + 2H2 (g) → CH3OH (g)

and I am asked to solve for the heat of reaction at 800 C. My query is the following: when finding the heat of reaction at standard state, which heat of formation I should use for the methanol? The heat of formation for gaseous or for liquid methanol?

The reason I may argue for liquid is because at standard state, methanol exists as a liquid. On the other hand, the reaction gives it as a gas. Which one do I choose and why? What's the rule about this sort of situation?