# Lithium hydride

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Lithium hydride
Identifiers
CAS number 7580-67-8
Properties
Molecular formula LiH
Molar mass 7.95 g mol−1
Appearance colorless to gray solid
Density 0.82 g cm−1, solid
Melting point

692 °C

Solubility in water Reacts
Hazards
EU classification Flammable (F)
Related compounds
Other cations sodium hydride, potassium hydride
Related compounds lithium borohydride, lithium aluminium hydride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lithium hydride (Li H) is the compound of lithium and hydrogen. It is a colourless crystalline solid, although commercial samples appear gray. Characteristic of a salt-like hydride, it has a high melting point (689 °C or 1272 ° F). Its density is 780 kilograms per cubic metre. It has a standard heat capacity of 29.73 J/mol*k with thermal conductivity that varies with composition and pressure (from at least 10 to 5 W/m*K at 400 K) and decreases with temperature.

It is a flammable solid and very reactive with water, producing the corrosive compound lithium hydroxide as well as hydrogen.

LiH + H2O → LiOH + H2

## Synthesis

It is produced by reacting lithium metal with hydrogen gas:

2 Li + H2 $\rightarrow$ 2 LiH

## Uses

LiH has numerous uses, as a desiccant, as a precursor for the synthesis of lithium aluminium hydride, in hydrogen generators, as both a coolant and shielding in nuclear reactors, and in the manufacture of ceramics. LiH has the highest hydrogen content (in mass percentage) of any saline hydride. The hydrogen content of LiH is three times that of NaH (though its stoichiometry is identical), because lithium is lighter than sodium, making LiH of interest for hydrogen storage.

The corresponding lithium deuteride, formula LiD, is the fusion fuel in thermonuclear weapons. In warheads of the Teller-Ulam design, LiD is compressed and heated by the explosion of the fission primary to the point where fusion occurs. Lithium deuteride, unlike tritium, is non-radioactive.

## Safety

LiH is flammable in air, and it reacts explosively with water to give corrosive LiOH together with hydrogen gas.

## In popular culture

In Larry Niven's science fiction book Protector, his character Brennan describes the by-products of a bussard ramjet as being an assortment of strange chemicals including "Lithium Hydride... a normally impossible chemical..." The book was published in 1973.