Reactions of molecules on solid surfaces are the basis for many industrial chemical processes, including semiconductor processing, corrosion, electrochemistry, and heterogeneous catalysis. A central industrial process in heterogeneous catalysis is ammonia synthesis. On ruthenium, one of the most active catalysts for ammonia synthesis, the rate-determining step is the dissociation of molecular nitrogen. There have been numerous experimental and theoretical studies on the energetics of this process. Surface science techniques such as reactive scattering, molecular beam, and laser-assisted associated desorption have measured dissociation probabilities and energy barriers of N 2 on Ru(0001). For these surface catalytic reactions, density functional theory (DFT) is widely used to predict reaction energies and activation barriers. Early DFT studies of N 2 on Ru(0001) have computed dissociation free energy barriers based on normal mode analysis with the harmonic approximation (HA) and showed reasonable agreement with thermal rate experiments. These calculations require the predetermination of local minima and transition states of the potential energy surface (PES) but do not capture anharmonic contributions. Within surface science, a standard practice for computing free energies is to use a single, lowest-energy configuration for each critical state and the normal modes of only the adsorbed atoms (i.e., adsorbate) excluding the surface atoms. However, recent theoretical and experimental investigations of larger reacting molecules or structurally complex catalytic materials, like metal organic frameworks (MOFs), have reported appreciable entropic contributions to the reaction barriers and rates beyond standard HA, such as configurational multiplicity and anharmonicity. These findings suggest that extending free energy calculations beyond the conventional harmonic approach is essential for predicting free energy barriers and determining the reactive configurations.