consist entirely of carbon skeletons bonded to H atoms since they have no ... We refer to alkanes as hydrocarbons because they contain only C (carbon) and ..... higher than that of staggered ethane, we can assign an energy value of 12 kJ/mol Solution consist entirely of carbon skeletons bonded to H atoms since they have no ... We refer to alkanes as hydrocarbons because they contain only C (carbon) and ..... higher than that of staggered ethane, we can assign an energy value of 12 kJ/mol.