1. The problem statement, all variables and given/known data The standard enthalpy of formation of the metallocene bis(benzene) chromium was measured in a calorimeter. It was found for the reaction [itex] Cr(C_6H_6)_2(s) --> Cr(s) + 2(C_6H_6)(g) [/itex] that [itex] \Delta_r U~at~583 K = +8.0 kJ/mol [/itex]. Find the corresponding reaction enthalpy and estimate the standard enthalpy of formation of the compound at 583 K. The constant-pressure molar heat capacity of benzene is 136.1 J/K mol in its liquid range and 81.67 J/K mol as a gas. 2. Relevant equations [itex] \Delta H = delta U +\Delta nRT [/itex] ??? 3. The attempt at a solution The first part is easy, [itex] \Delta H = +17.7 kJ/mol [/itex]. I'm at a complete loss for estimating the standard enthalpy of formation. I've tried using Kirchoff's rule including phase change enthalpy and my result is +110.8 kJ/mol. I've tried other less sensible ways but those solutions are even further from the textbook answer of +116.0 kJ/mol. I used Kirchoffs rule for C6H6(l) --> C6H6(g) with [itex] \Delta_r H = 49.0 kJ/mol [/itex] for C6H6(l). The enthalpy of vaporization is 30.8 kJ/mol. I'm tired right now and don't want to type out all of my work. I'll do it tomorrow when I wake up. If anyone wants to help before then I thank you.