Lithium hydride

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Lithium hydride

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LiHcrack

Lithium hydride (LiH) is an inorganic compound that is formed by the direct combination of lithium (Li) and hydrogen (H) atoms. It is a colorless crystalline solid, although, like many lithium compounds, it can present in different colors depending on impurities. Lithium hydride is used primarily as a strong base in organic synthesis and as a hydrogen storage medium. Its properties and applications make it an important compound in both chemistry and material science.

Properties

Lithium hydride is a saline (ionic) hydride, composed of Li^+ and H^- ions. It has a high melting point of approximately 689°C (1272°F) and is highly soluble in anhydrous hydronium solutions but reacts violently with water to form lithium hydroxide (LiOH) and hydrogen gas (H2). This reaction with water releases a significant amount of energy, making LiH hazardous in moist environments. Additionally, LiH has a high specific heat capacity and thermal conductivity, properties that are beneficial in its use as a heat storage medium.

Synthesis

Lithium hydride is synthesized through a direct combination reaction where lithium metal is reacted with hydrogen gas at temperatures around 600°C (1112°F). The reaction is highly exothermic:

\[2 \, \text{Li} + \text{H}_2 \rightarrow 2 \, \text{LiH}\]

This process requires careful control of temperature and the exclusion of moisture to prevent unwanted side reactions.

Applications

Hydrogen Storage

Lithium hydride is used as a means of storing hydrogen due to its high hydrogen content by weight. It can release hydrogen upon heating, making it a potential material for hydrogen fuel storage in fuel cell applications. However, the high temperature required to release the hydrogen and its reactivity with water are challenges that need to be addressed for practical applications.

Chemical Synthesis

In organic chemistry, LiH is utilized as a strong base for the deprotonation of alcohols, amines, and other acidic organic compounds. It is also used in the synthesis of specific hydrides, such as sodium borohydride (NaBH4), which is an important reducing agent in organic synthesis.

Nuclear Physics

Due to its high neutron absorption cross-section, lithium hydride has been studied as a potential material for nuclear fusion reactors, particularly in designs that require solid neutron moderators. However, its application in this area is limited by its reactivity and the difficulty in handling.

Safety

Lithium hydride is highly reactive, especially with water, and can pose a fire and explosion hazard. It requires careful handling, storage under inert atmosphere, and rigorous safety precautions to prevent accidental exposure to moisture. Proper personal protective equipment (PPE) and training are essential for those handling LiH.

See Also

• Lithium
• Hydrogen
• Inorganic compound
• Hydrogen storage
• Nuclear fusion