4 HCl (aq) + MnO₂ (s) → MnCl₂ (aq) + Cl₂ (g) + 2 H₂O (l)

This is an oxidation-reduction (redox) reaction:

MnO₂ is an oxidizing agent, HCl is a reducing agent.

Reactants:

• HCl – Chlorane , Hydrogen chloride
  • Other names: Hydrochloric acid , M , Uriatic acid ... show moreHydronium chloride , Chlorhydric Acid , Hydrochloric acid gas , HCl , Anhydrous hydrogen chloride , Hydrochloric acid, anhydrous , Aqueous hydrogen chloride , [Note: Often used in an aqueous solution.] show less
  • Appearance: Colorless, transparent liquid, fumes in air if concentrated ; Colorless gas ; Colourless compressed liquefied gas with pungent odour ; Colorless to slightly yellow gas with a pungent, irritating odor. [Note: Shipped as a liquefied compressed gas.]
• MnO₂ – Manganese oxide , Manganese(IV) oxide
  • Other names: Manganese dioxide , Pyrolusite , Hyperoxide of manganese ... show moreBlack oxide of manganese , Manganic oxide , MnO2 , MnO₂ , Manganese(IV)oxide , Manganese peroxide show less
  • Appearance: Brown-black solid ; Black-to-brown powder

Products:

• MnCl₂ – Manganese(II) chloride , Manganese dichloride
  • Other names: Manganous chloride , Manganous dichloride , Manganese(II) chloride (1:2) ... show moreManganese bichloride , Manganese chloride anhydrous , Manganese chloride , Manganese(II) dichloride show less
  • Appearance: Pink solid (tetrahydrate)
• Cl₂
  • Names: Chlorine , Molecular chlorine
  • Appearance: Greenish-yellow compressed liquefied gas with pungent odour ; Greenish-yellow gas with a pungent, irritating odor. [Note: Shipped as a liquefied compressed gas.]
• H₂O – Water, oxidane
  • Other names: Water (H2O) , Hydrogen hydroxide (HH or HOH) , Hydrogen oxide ... show moreDihydrogen monoxide (DHMO) (systematic name) , Hydrogen monoxide , Dihydrogen oxide , Hydric acid , Hydrohydroxic acid , Hydroxic acid , Hydrol , Μ-oxido dihydrogen , Κ1-hydroxyl hydrogen(0) show less
  • Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas