By performing work function change (Delta WF) measurements, we characterized thermal stability and desorption of cobalt phthalocyanine (CoPc) molecules on the Ag(100) surface from sub-monolayer to multilayer coverages. Based on the temperature dependence of the Delta WF we were able to determine the desorption temperature from multilayer. Obtained dependences of Delta WF and a low-energy electron reflectivity (R) for sub-and monolayer reveal that layers with contact with Ag(100) have higher thermal stability and their desorption is accompanied by decomposition of CoPc molecule. Exploring the time evolutions of the Delta WF at various temperatures allowed us to establish effective activation energies and effective frequency prefactors for processes occurring at various temperatures. The effective activation energies remain almost the same, from sub-monolayer to multilayer (2.97 eV -2.62 eV), whereas the frequency prefactors vary from 10(13) s(-1) (monolayer) to 10(24) s(-1) (multilayer). For multilayer only desorption occurs, whereas for layers in contact with reactive Ag(100) surface (monolayer) the decomposition occurs at the same temperature range as desorption. Low-energy electron diffraction was used to describe CoPc molecular arrangements. To the best of our knowledge, we are the first who have observed (5 x 5) R +/- 37 degrees structure for CoPc on Ag(100). (c) 2017 Elsevier B.V. All rights reserved.