3 K2MnO4 + 2 H2O → 2 KMnO4 + MnO2 + 4 KOH

This is an oxidation-reduction (redox) reaction:

2 MnVI - 2 e- → 2 MnVII (oxidation)

MnVI + 2 e- → MnIV (reduction)

K2MnO4 is both an oxidizing and a reducing agent (disproportionation (dismutation)).

Reactants:

  • K2MnO4 – Potassium manganate(VI) source: wikipedia, accessed: 2019-09-27
    • Other names: Potassium manganate source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02
    • Appearance: Green crystals (darkening with time) source: wikipedia, accessed: 2019-09-27
  • H2O – Water, oxidane source: wikipedia, accessed: 2019-09-27
    • Other names: Water (H2O) source: wikipedia, accessed: 2019-09-27, Hydrogen hydroxide (HH or HOH) source: wikipedia, accessed: 2019-09-27, Hydrogen oxide source: wikipedia, accessed: 2019-09-27
    • Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas source: wikipedia, accessed: 2019-09-27

Products:

  • KMnO4 – Potassium manganate(VII) source: wikipedia, accessed: 2019-09-27
    • Other names: Potassium permanganate source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, Chameleon mineral source: wikipedia, accessed: 2019-09-27, Condy's crystals source: wikipedia, accessed: 2019-09-27
    • Appearance: Purplish-bronze-gray needles | magenta–rose in solution source: wikipedia, accessed: 2019-09-27; Dark purple crystals source: ICSC, accessed: 2019-09-04
  • MnO2 – Manganese oxide source: wikipedia, accessed: 2019-09-27, Manganese(IV) oxide source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02
    • Other names: Manganese dioxide source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, Pyrolusite source: wikipedia, accessed: 2019-09-27, Hyperoxide of manganese source: wikipedia, accessed: 2019-09-27
    • Appearance: Brown-black solid source: wikipedia, accessed: 2019-09-27; Black-to-brown powder source: ICSC, accessed: 2019-09-04
  • KOH – Potassium hydroxide source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02
    • Other names: Caustic potash source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02, Lye source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02, Potash lye source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02
    • Appearance: White solid, deliquescent source: wikipedia, accessed: 2019-09-27; White hygroscopic solid in various forms source: ICSC, accessed: 2019-09-04; Odorless, white or slightly yellow lumps, rods, flakes, sticks, or pellets. [Note: May be used as an aqueous solution.] source: NIOSH NPG, accessed: 2019-09-02