3 Se + 4 HNO3 + H2O → 3 H2SeO3 + 4 NO

This is an oxidation-reduction (redox) reaction:

3 Se0 - 12 e- → 3 SeIV (oxidation)

4 NV + 12 e- → 4 NII (reduction)

Se is a reducing agent, HNO3 is an oxidizing agent.

Reactants:

  • Se
    • Names: Selenium source: wikidata, accessed: 2019-09-07source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02, Se source: wikidata, accessed: 2019-09-07, Selen source: wikidata, accessed: 2019-09-07
    • Appearance: Grey solid in various forms source: ICSC, accessed: 2019-09-04; Amorphous or crystalline, red to gray solid. [Note: Occurs as an impurity in most sulfide ores.] source: NIOSH NPG, accessed: 2019-09-02
  • HNO3 – Nitric acid source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: NIOSH NPG, accessed: 2019-09-02
    • Other names: Aqua fortis source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: NIOSH NPG, accessed: 2019-09-02, Spirit of niter source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02, Eau forte source: wikipedia, accessed: 2019-09-27
    • Appearance: Colorless, yellow or red fuming liquid source: wikipedia, accessed: 2019-09-27; Colourless-to-yellow liquid with pungent odour source: ICSC, accessed: 2019-09-04; Colorless, yellow, or red, fuming liquid with an acrid, suffocating odor. [Note: Often used in an aqueous solution. Fuming nitric acid is concentrated nitric acid that contains dissolved nitrogen dioxide.] source: NIOSH NPG, accessed: 2019-09-02
  • 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:

  • H2SeO3 – Selenous acid source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, Selenic(IV) acid source: wikipedia, accessed: 2019-09-27
    • Other names: Selenious acid source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: ICSC, accessed: 2019-09-04, [SeO(OH)2] source: wikidata, accessed: 2019-09-02, Selenige Säure source: wikidata, accessed: 2019-09-02, Monohydrated selenium dioxide source: ICSC, accessed: 2019-09-04
    • Appearance: White hygroscopic crystals source: wikipedia, accessed: 2019-09-27; Colourless hygroscopic crystals source: ICSC, accessed: 2019-09-04
  • NO – Nitrogen monoxide source: wikipedia, accessed: 2019-09-27source: wikidata, accessed: 2019-09-02source: NIOSH NPG, accessed: 2019-09-02, Oxidonitrogen(•) (additive) source: wikipedia, accessed: 2019-09-27
    • Other names: Nitric oxide source: wikipedia, accessed: 2019-09-27source: ICSC, accessed: 2019-09-04source: NIOSH NPG, accessed: 2019-09-02source: wikidata, accessed: 2019-09-02, Nitrogen(II) oxide source: wikipedia, accessed: 2019-09-27, Nitric oxide (radical) source: wikidata, accessed: 2019-09-02
    • Appearance: Colourless gas source: wikipedia, accessed: 2019-09-27; Colourless compressed gas source: ICSC, accessed: 2019-09-04; Colorless gas. [Note: Shipped as a nonliquefied compressed gas.] source: NIOSH NPG, accessed: 2019-09-02