The conclusion that enthalpic effects are more important than entropic effects is hardly surprising. Nevertheless, the present work provides some useful context in the consideration of coveragedependent entropy. The impact of lateral interactions on vibrational entropy is expected to be important for large-amplitude, low-frequency normal modes, such as those that describe the frustrated diffusion and libration parallel to the surface. The impact is expected to be dependent on both the binding energy and the binding site. As the surface coverage increases, repulsive interactions should lead to a crowding effect that should reduce the area available for large-amplitude motion, thereby increasing the vibrational frequency and thus decreasing the entropy. In some instances, however, the opposite effect occurred; the increased crowding caused a shift to other binding sites with lower frequency modes, thereby increasing the vibrational entropy. Hence, the vibrational entropy for loosely bound adsorbates could be highly dependent on coverage. Similarly, for an adsorbate with a strong dipole moment such as SO 2 , the coverage effect on lateral motion frequencies is anticipated to be much greater. Additionally, it will also be necessary to include cross interactions in the form of higher-order terms into the coverage-dependence thermochemistry model to achieve a more accurate description of the enthalpy and entropy at high coverages , which is the subject of future work. More generally, the present work provides a better conceptual understanding of the interplay between lateral interactions and entropy. Based upon the present work, we conclude that the significance of coverage-dependent entropy is constrained by thermodynamics at both low and high temperatures. At low temperatures, the surface is completely saturated and coverage effects are critical. However, at low-temperature conditions, the free energy is dominated by enthalpy, and entropic considerations are generally negligible. Conversely, at high temperatures, entropic effects can be the dominant term for the free energy, but the coverage is expected to be low because the dominant driving force is desorption. Accordingly, there is a narrow window in which the temperature is high enough that entropic effects are important, but low enough that the surface is still crowded. The limits of this window will be system specific.