© 2022, TUBITAK. All rights reserved.In the present study, we have theoretically obtained the enthalpies and activation energies of several gas reactions by Intrinsic Reaction Coordinate (IRC) calculations. Being a first time, the approximate transition states used in the IRC calculations were obtained from the saddle points on the two dimensional Potential Energy Surface (PES) scans trucking the pathway of the reactions. In all the calculations, the Density Functional Theory (DFT/B3LYP) with 6-31 G (d, p) level was used. The saddle points on the PES graphs of the reactions were used one by one as an approximate transition state (TS) in the IRC calculations until the appropriate reaction path was obtained. The obtained TS’s from the IRC calculations were tested for having only one imaginary frequency. The energy diagram schemes showing the reactants, products, and transition states of all the reactions were drawn, and their enthalpies and activation energies were determined. From the enthalpy values it was decided whether the reactions are endothermic or exothermic. The calculated activation energies were compared with the ones in the literature.