In our attempts to understand and control the activity at electrochemical interfaces, first-principles calculations based on density functional theory prove invaluable in providing atomistic descriptions of such interfacial chemistry. Furthermore, recent advances in X-ray spectroscopy enable in situ examination of working cells with both interfacial and chemical sensitivity. Interpretation of such measurements benefits greatly from exploration of possible chemistry at reactive surfaces and direct simulation of spectra based on molecular dynamics sampling. We combine insight from continuum modeling of electrolytes next to charged electrodes with first-principles determinations of free-energy profiles of electrolyte species at specific electrode surfaces. In this way, we aim to have models consistent with thermodynamic boundary conditions at charged interfaces. We provide examples relevant to chemically reactive electrodes, and elucidation of speciation in the electric double layer, which can inspire strategies to enhance performance in new electrochemical systems or simply increase our understanding of atomic scale mechanisms behind electrochemical processes.