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Water-reactive substances [1] are those that spontaneously undergo a chemical reaction with water, often noted as generating flammable gas. [2] Some are highly reducing in nature. [ 3 ] Notable examples include alkali metals , lithium through caesium , and alkaline earth metals , magnesium through barium .
The most reactive metals, such as sodium, will react with cold water to produce hydrogen and the metal hydroxide: 2 Na (s) + 2 H 2 O (l) →2 NaOH (aq) + H 2 (g) Metals in the middle of the reactivity series, such as iron , will react with acids such as sulfuric acid (but not water at normal temperatures) to give hydrogen and a metal salt ...
The alkali metals also react with water to form strongly alkaline hydroxides and thus should be handled with great care. The heavier alkali metals react more vigorously than the lighter ones; for example, when dropped into water, caesium produces a larger explosion than potassium if the same number of moles of each metal is used.
Metal aqua ions are often involved in the formation of complexes. The reaction may be written as pM x+ (aq) + qL y− → [M p L q] (px-qy)+ In reality this is a substitution reaction in which one or more water molecules from the first hydration shell of the metal ion are replaced by ligands, L. The complex is described as an inner-sphere complex.
Reaction with nitrogen. Only Be and Mg form nitrides directly. 3Be + N 2 → Be 3 N 2 3Mg + N 2 → Mg 3 N 2. Reaction with hydrogen. Alkaline earth metals react with hydrogen to generate saline hydride that are unstable in water. Ca + H 2 → CaH 2. Reaction with water. Ca, Sr, and Ba readily react with water to form hydroxide and hydrogen gas.
Potassium metal can react violently with water producing KOH and hydrogen gas. 2 K(s) + 2 H 2 O(l) → 2 KOH(aq) + H 2 (g)↑ A reaction of potassium metal with water. Hydrogen is produced, and with potassium vapor, burns with a pink or lilac flame. Strongly alkaline potassium hydroxide is formed in solution.
Addition of a small amount of caesium to cold water is explosive. Caesium metal is highly reactive and pyrophoric. It ignites spontaneously in air, and reacts explosively with water even at low temperatures, more so than the other alkali metals. [14] It reacts with ice at temperatures as low as −116 °C (−177 °F). [17]
The alkali metals react with oxygen to form several different compounds: suboxides, oxides, peroxides, sesquioxides, superoxides, and ozonides. They all react violently with water. They all react violently with water.