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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 metal reacts with the water first, breaking the hydrogen bonds in the water and producing hydrogen gas; this takes place faster for the more reactive heavier alkali metals. Second, the heat generated by the first part of the reaction often ignites the hydrogen gas, causing it to burn explosively into the surrounding air.
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 ...
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]
Bulk sodium is usually stored in oil or an inert gas. Sodium metal can be easily cut with a knife. It is a good conductor of electricity and heat. Due to having low atomic mass and large atomic radius, sodium is third-least dense of all elemental metals and is one of only three metals that can float on water, the other two being lithium and ...
Both factors are actually distinct, and both commonly depend on temperature. For example, it is commonly asserted that the reactivity of alkali metals (Na, K, etc.) increases down the group in the periodic table, or that hydrogen's reactivity is evidenced by its reaction with oxygen. In fact, the rate of reaction of alkali metals (as evidenced ...
Plutonium is a reactive metal. In moist air or moist argon, the metal oxidizes rapidly, producing a mixture of oxides and hydrides. [5] If the metal is exposed long enough to a limited amount of water vapor, a powdery surface coating of PuO 2 is formed. [5] Also formed is plutonium hydride but an excess of water vapor forms only PuO 2. [41]
When finely powdered, magnesium reacts with water to produce hydrogen gas: Mg(s) + 2 H 2 O(g) → Mg(OH) 2 (aq) + H 2 (g) + 1203.6 kJ/mol However, this reaction is much less dramatic than the reactions of the alkali metals with water, because the magnesium hydroxide builds up on the surface of the magnesium metal and inhibits further reaction.