7.75b reaction states

[104341943]

In 7.75 it gives us CH3OH, and we are to find the enthalpy. When writing the reaction equation, how do we know that the reactants are in the gas phase?

[Chem_Mod]

Enthalpy of formation relates to the formation of the compound from its elements in their most stable forms. Most elemental compounds are most stable as diatomic gases, such as H₂ and N₂.

All bond enthalpies relate to breaking the bonds of a compound in its gas phase.

[Denise 3L]

For this same question, the solutions manual also inserts a number to atomize C(gr) at 717kj/mol, where did they find this number, I don't see it in the 3 tables, and what does it mean?

[Niharika Reddy 1D]

That value is the enthalpy of sublimation of carbon, and it is found in the problem itself. Enthalpy of sublimation is the molar enthalpy change when a solid converts directly into a gas.

[Denise 3L]

Oh my eyes totally flew past that part, great thank you!

[Chem_Mod]

In this problem you are asked to calculate standard enthalpies of formation from information given in several tables. For CH3OH (methanol) the elements that form it are carbon ("C", solid, given the enthalpy of formation in the problem), oxygen (O2, gas), and hydrogen (H2, gas). The standard states for several molecules are given in the periodic table such as nitrogen (gas), fluorine, (gas), bromine (liquid), and iodine (liquid). However, I would suggest looking at the table for bond energies to successfully complete this problem and calculate the enthalpies of the reactions (in this case formation of the compounds from its elements).