This is an acid-base reaction (neutralization): FeO is a base, HCl is an acid.
Reactants:
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FeO – Iron(II) oxide
Other names: Ferrous oxide, Iron monoxide, Iron oxide
Appearance: Black crystals ; Black solid in various forms
HCl – Chlorane, Hydrogen chloride
Other names: Hydrochloric acid, M, Uriatic acid
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.]
Products:
FeCl2 – Iron(II) chloride, Iron dichloride
Other names: Ferrous chloride, Rokühnite, [FeCl3], FeCl3
Appearance: Tan solid (anhydrous) | Pale green solid (di-tetrahydrate) ; White-to-light-green hygroscopic crystals
H2O – Water, oxidane
Other names: Water (H2O), Hydrogen hydroxide (HH or HOH), Hydrogen oxide
Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas