Potassium pentasulfide

Potassium pentasulfide is the inorganic compound with the formula K2S5. It is a red-orange solid that dissolves in water. The salt decomposes rapidly in air. It is one of several polysulfide salts with the general formula M2S_{n}, where M = Li, Na, K and n = 2, 3, 4, 5, 6. The polysulfide salts of potassium and sodium are similar.

Preparation and reactions
The salt is prepared by the addition of elemental sulfur to potassium sulfide. An idealized equation is shown for potassium hydrosulfide:
 * 4 KSH + S8 → 2 K2S5 + 2 H2S

The structure consists of zigzag chains of S5(2−) paired with K+ ions.

Occurrence
Various polysulfides K2S2 - K2S6 are components of liver of sulfur. Polysulfides, like sulfides, can induce stress corrosion cracking in carbon steel and stainless steel.