Potassium reacting with water. Water being dripped into adish containing potassium metal. Potassium (chemical symbol K) is a silver-white, alkali metal. It reacts violently and exothermically (generating heat) with water (chemical symbol H2O), yielding potassium hydroxide (KOH) and hydrogen gas (H2). The reaction is explosive because the generated heat causes the hydrogen to ignite. The chemical equation for this reaction is: 2K + 2H2O ----> 2KOH + H2 Potassium metal is usually stored under kerosene because it oxidizes when exposed to air.