Na2S2O3 + I2 = NaI + Na2S4O6

Balanced Chemical Equation – Solution

2Na2S2O3 + I2 → 2NaI + Na2S4O6

The coefficients show the number of particles (atoms or molecules), and the indices show the number of atoms that make up the molecule. New substances are formed as a result of the rearrangement of the original atoms. As a result of a chemical reaction, atoms of chemical elements do not disappear anywhere and new ones do not appear, their number remains unchanged – this follows from the law of conservation of mass of substances.

Chemical Reaction Information

Sodium Thiosulfate + Diiodine = Sodium Iodide + Sodium Tetrathionate

This is an oxidation-reduction (redox) reaction. Na2S2O3 is a reducing agent, I2 is an oxidizing agent.

  • 4 SII  2 e  4 S5/2 (oxidation)
  • 2 I0 + 2 e  2 I-I (reduction)

Reaction Type

Double Displacement (Metathesis)

Substances that react are called starting materials or reactants. The substances that form as a result are called reaction products.



  • Names: Sodium thiosulfate.
  • Appearance: White crystals.


  • Names: Iodine.
  • Appearance: Bluish black or dark purple crystals with pungent odour.



  • Names: Sodium iodide.
  • Appearance: White solid | deliquescent.


  • Names: Sodium tetrathionate.
Similar Examples of Equalizing a Chemical Reaction
I2 + Na2S2O3 → NaI + NaS4O6
I2 + Na2S2O3 → NaI + Na2S4O6
H2O + I2 + Na2S2O3 → HI + NaHSO4
NaOH + I2 + Na2S2O3 → H2O + Na2SO4 + NaI
I2 + Na2S2O3 → Na2S4O6 + NaI2

Alexander Stephenson

Candidate of Chemical Sciences, editor-in-chief of Lecturer at several international online schools, member of the jury of chemistry competitions and author of scientific articles.

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