It is difficult to prepare many compounds directly from the elements，so values for these compounds cannot be measured directIy. For many organic compounds，it is easier to measure the standard enthalpy of combustion by reaction of the compounds with excess O 2 (g) to form CO 2 (g) and H 2 O(l). From the following standard enthalpies of combustion at 298.15K，determine for the compound． (1)cyclohexane，C 6 H 12 (l)，a useful organic solvent： =-3920kJ·mol -1 (2)phenol，C 6 H 5 OH(s)，used as a disinfectant and in the production of thermo-setting plastics： =-3053kJ·mol -1