In order to explore to what extent equilibrium adsorption can be studied with surface science methods such as reflection absorption infrared spectroscopy (RAIRS), static secondary ion mass spectroscopy (SSIMS) and X-ray photoelectron spectroscopy (XPS), adsorption of CO on a Rh(1 0 0) single crystal surface has been studied. A structural model of CO on Rh(1 0 0) at different coverages is presented. Under equilibrium adsorption conditions, we were able to determine the CO coverage and adsorption isotherms. From the isotherms, an isosteric heat of adsorption of about 160 kJ/mol was obtained, compared to an activation energy of desorption of 132 kJ/mol from temperature programmed desorption (TPD) experiments. (C) 2009 Elsevier B.V. All rights reserved.