The process of complexation molybdenum (V) with 1-phenyl-2,3-dimethylpyrazolin-5-thione in a 4 mol/l HCI medium the temperature range 273-338 K was studied by potentiometric method. It has been shown that reduced form molecule is involved complex formation reaction. Using data studies, change energy value (ΔE) (NH ) 2 [MoOCI 5 ] -1-phenyl-2,3-dimethylpyrazolin-5-thione-4 HCl system, equilibrium...