1. The problem statement, all variables and given/known data Imagine a hypothetical process in which the methane molecule, CH4, is "expanded," by simultaneously extending all four C−H bonds to infinity. We then have the process: CH4 (g) → C(g) + 4H(g) Compare the reaction for the "expansion" of methane with the reverse of the reaction that represents the standard enthalpy of formation. Is the state of the carbon atoms the same or different when reversed? 2. Relevant equations None 3. The attempt at a solution According to my assignment, the state of the carbon atoms is different when the reaction is reversed. I don't understand why Carbon is a gas when decomposed from CH4, but a solid when combined with hydrogen to form CH4. I understand that Carbon is a solid at room temperature, but then why would the decomposition result in gaseous Carbon rather than solid Carbon?