Gas detecting and sensing is a largely studied field of knowledge, but total understanding is not yet achieved and the ideal device is still far in the future. Many experimental efforts have been devoted to find the minimum optimal temperature and operational conditions for SnO2 to sense hydrocarbons; different methods to build gas-detecting devices keep being developed all around the world, from paste-based bulk devices to nanostructured thick and thin films, but little effort has been aim to characterize the reactions by calculating their related enthalpies. Computational methods have been widely used to characterize, understand and model many physicochemical interactions. In this regard, three main courses can be followed: Ab initio (first principles of quantum mechanics), DFT (Density Functional Theory) and MD (Molecular Dynamics) simulation. In this research, DFT modelling tool is employed to understand and characterize the gas-sensing reactions of Tin Oxide when exposed to an atmosphere with Methane. In CASTEP, a robust DFT module of the Materials Studio suite, one SnO2 (110) crystal plane is exposed to CH4 and the structure is optimized many times for each possible step of the reaction, recording the energies related with each optimization stage, in sum giving us the Transition State (TS) of the reaction. Based on the data, a promising reaction-path is proposed and analyzed for the (110) surface.