The results are different for CO adsorbed on Co(0001) in Figure . Due to the attractive interactions at a coverage of 1/3 ML, the equilibrium constant first increases with increasing coverage before the repulsive interactions become dominating. The impact of entropy is much more pronounced. An omission of coverage dependence leads to an equilibrium constant that deviates by orders of magnitude at high coverages. The importance of accurately quantifying the attractive interactions at medium coverages becomes apparent when comparing the relative equilibrium constants in Figure . The formation of the stabilized ( √ 3 × √ 3)R30 • -CO islands increases the adsorption equilibrium constant by a factor of 3-7, depending on the temperature when coverage effects for the enthalpy and entropy are considered. Without the inclusion of a coverage-dependent entropy, K eq increases only by a factor 1.5-2.2. The inclusion of the entropy effects for the accurate modeling of the CO coverage on Co(0001) is crucial since the * CO coverage controls the chain growth in the Fischer-Tropsch process .