It is known that the production reaction of sodium thiosulfate which consists of the reaction of Na 2 SO 3 with sulfur is considerably slow. Ultrasound energy was used to increase the conversion fraction of sulfur and to accelerate the production reaction of Na 2 S 2 O 3 , and the effect of ultrasonic energy on the reaction kinetics was investigated. The particle size, reaction temperature, concentration of Na 2 SO 3 solution and amplitude of ultrasound power were chosen as parameters. The experiments were performed in the absence and presence of ultrasound. Considering the results the reaction is chemically controlled first order and the activation energy is equal to 42 kJ/mol in both cases. The results indicated that the ultrasound energy increased the reaction speed but it did not vary the activation energy. The effect of ultrasound is on the pre-exponential factor A. Finally, an empirical relation is given which relates the rate constant to ultrasound power.

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