Ethanol decomposition over Pd(111) has been systematically investigated using self-consistent periodic density functional theory, and the decomposition network has been Mapped Out. The most. stable adsorption of the involved species tends to fellow the gas-phase bond order rules, wherein C is tetravalent and O is divalent with the missing H atoms replaced by metal atoms. Desorption is preferable for adsorbed ethanol, methane, and CO, while for the other species decomposition is preferred. For intermediates going, along the decomposition pathways, energy barriers for the C-C, C-alpha-H, and O-H scissions are decreased, while it is increased for the C-O path or changes less for the C-beta-H path. For each of the C-C, C-O, and C-H paths, the Bronsted-Evans-Polanyi relation holds roughly. The most likely decomposition path is CH3CH2OH -> CH3CHO -> CH3CHO -> CH3CO -> CH2CO -> CHCO -> CH + CO -> CO + H + CH4 + C.