Rhenium

Rhenium does not dissolve in hydrochloric acid (HCl) and hydrofluoric acid (HF). It does dissolve in nitric acid, HNO₃, and concentrated sulphuric acid, H₂SO4, forming solutions of perrhenic acid, HReO₄.

Rhenium reacts slowly with oxygen, O₂, tarnishing the surface, under normal conditions. If heated, rhenium is oxidized to Re(VII) oxide:

4 Re(s) + 7 O₂(g) 2 Re₂O₇(s)

Rhenium will react with F₂ when heated, forming a mixture of rhenium(VI) fluoride and rhenium(VII) fluoride. At 400 °C and under pressure, only rhenium(VII) fluoride is formed.

Re(s) + 3 F₂(g) ReF₆(s)
2 Re(s) + 7 F₂(g) 2 ReF₇(s)

Rhenium reacts with water [1]:

Re(s) + 2 H₂O(l) ReO₂(s) + 4 H⁺(aq) + 4 e⁻                   E° = -0.251 V
Re³⁺(aq) + 3 H₂O(l) ReO₃(s) + 6 H⁺(aq) + 3 e⁻              E° = -0.318 V
Re³⁺(aq) + 4 H₂O(l) ReO₄²⁻(aq) + 8 H⁺(aq) + 3 e⁻         E° = -0.795 V
Re³⁺(aq) + 4 H₂O(l) ReO₄⁻(aq) + 8 H⁺(aq) + 4 e⁻           E° = -0.422 V