The rate of reaction between nitrosyl ferrous ethylenediaminetetramethy-lenephosphonate and sodium sulfite in aqueous solutions was measured spec-trophotometrically at temperatures ranging from 20 to 35℃ and over the pH range 5.57 to 7.48 with the aid of a rapid mixing device. The FeII (EDTMP) (NO) solution

prepared by introducing nitric oxide into FeII (EDTMP)solution

was mixed instantaneously with sodium sulfite solution. Then the sequential change in absorbance of the solution at 590-600 nm was scanned. The reaction was of second order at pH 5.88 and I = 0.3 mol/l.The reaction rate constant k at 20

25

30 and 35℃ was determined to be 1.95

3.03

5.48 and 7.05 l/(mol. min)

respectively. The apparent activation- energy for this reaction was calculated to be 68.6kJ/mol

which was smaller than that of the-FeII(EDTA)(NO)system(102.9 kJ/mol at pH 5.97). The dependence of the reaction rate on pH was discussed.