# Should temperature and pressure conditions for two reactions be same for them to combine for enthalpy calculations?

I was solving a question in which I had to calculate Enthalpy of formation of $$\ce{CS_2(l)}$$ using the given Enthalpy of combustion (not in standard state) of $$\ce{C(s)}$$, $$\ce{S(s)}$$ and $$\ce{CS_2(l)}$$.

To calculate the $$\Delta H_f$$ of $$\ce{CS_2(l)}$$, we combine the corresponding equation of combustion of these chemicals in appropriate order to form the equation : $$\ce{C(s) + 2S(g) -> CS_2(l) }$$ Should the temperature and pressure conditions of the combustion equations be same for me to combine them mathematically?

• Yes, strictly speaking, they must be the same. Oct 5 '20 at 14:53