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Lithium hydride

Lithium hydride
Space-filling model of part of the crystal structure of lithium hydride
Identifiers
3D model (Jmol)
ChemSpider
ECHA InfoCard 100.028.623
PubChem CID
RTECS number OJ6300000
Properties
LiH
Molar mass 7.95 g/mol
Appearance colorless to gray solid
Density 0.78 g/cm3
Melting point 688.7 °C (1,271.7 °F; 961.9 K)
Boiling point decomposes at 900–1000 °C
reacts
Solubility slightly soluble in dimethylformamide
reacts with ammonia, diethyl ether, ethanol
−4.6·10−6 cm3/mol
1.9847
Structure
fcc (NaCl-type)
a = 0.40834 nm
6.0 D
Thermochemistry
3.51 J/(g·K)
170.8 J/mol K
-90.65 kJ/mol
-68.48 kJ/mol
Hazards
Safety data sheet ICSC 0813
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuel Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
200 °C (392 °F; 473 K)
Lethal dose or concentration (LD, LC):
LD50 (median dose)
 77.5 mg/kg (oral, rat)
22 mg/m3 (rat, 4 hr)
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 0.025 mg/m3
REL (Recommended)
 TWA 0.025 mg/m3
IDLH (Immediate danger)
 0.5 mg/m3
Related compounds
Other cations
Sodium hydride
Potassium hydride
Rubidium hydride
Caesium hydride
Related compounds
 Lithium borohydride
Lithium aluminium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Lithium hydride is an inorganic compound with the formula LiH. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like, or ionic, hydride, it has a high melting point and is not soluble but reactive with all organic and protic solvents; it is soluble and non-reactive with certain molten salts such as lithium fluoride, lithium borohydride, and sodium hydride. With a molecular mass of slightly less than 8, it is the lightest ionic compound.

LiH is a diamagnetic and an ionic conductor with a conductivity gradually increasing from 2×10−5 Ω−1cm−1 at 443 °C to 0.18 Ω−1cm−1 at 754 °C; there is no discontinuity in this increase through the melting point. The dielectric constant of LiH decreases from 13.0 (static, low frequencies) to 3.6 (visible light frequencies). LiH is a soft material with a Mohs hardness of 3.5. Its compressive creep (per 100 hours) rapidly increases from < 1% at 350 °C to > 100% at 475 °C meaning that LiH can't provide mechanical support when heated.

The thermal conductivity of LiH decreases with temperature and depends on morphology: the corresponding values are 0.125 W/(cm·K) for crystals and 0.0695 W/(cm·K) for compacts at 50 °C, and 0.036 W/(cm·K) for crystals and 0.0432 W/(cm·K) for compacts at 500 °C. The linear thermal expansion coefficient is 4.2×10−5/°C at room temperature.

LiH is produced by treating lithium metal with hydrogen gas:


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