A quantum theoretical study was done on two of benzimidazole derivatives to calculate the energetic behavior of the compounds in the gas phase, where (the density functional theory (DFT), Becke’s three-parameter exchange function and the Lee-Yang-Parr correlation function (B3LYP)) was considered to calculate the quantum chemical descriptors such as (the energy gap between HOMO and LUMO, the total energy, chemical hardness, softness, electrophilicity index, electro-negativity) calculations. Besides, a theoretical study was done for the compounds, which were in Gas-phase, in order to study and examine the effect of changing the temperature of the molecule which was from (200K to 1000K) on thermodynamics properties (Enthalpy, Entropy, Heat capacity, and correlation properties).