Lithium hydride
Lithium cation, Li+ Hydrogen anion, H− | |
__H− __Li+
Structure of lithium hydride. | |
Identifiers | |
---|---|
3D model (
JSmol ) |
|
ChemSpider | |
ECHA InfoCard
|
100.028.623 |
PubChem CID
|
|
RTECS number
|
|
UNII | |
CompTox Dashboard (EPA)
|
|
| |
| |
Properties | |
LiH | |
Molar mass | 7.95 g·mol−1 |
Appearance | colorless to gray solid[1] |
Density | 0.78 g/cm3[1] |
Melting point | 688.7 °C (1,271.7 °F; 961.9 K)[1] |
Boiling point | 900–1,000 °C (1,650–1,830 °F; 1,170–1,270 K) (decomposes)[2] |
reacts | |
Solubility | slightly soluble in dimethylformamide reacts with ammonia, diethyl ether, ethanol |
−4.6·10−6 cm3/mol | |
Refractive index (nD)
|
1.9847[3]: 43 |
Structure | |
NaCl-type )
| |
a = 0.40834 nm[3]: 56
| |
6.0 D[3]: 35 | |
Thermochemistry | |
Heat capacity (C)
|
3.51 J/(g·K) |
Std molar
entropy (S⦵298) |
170.8 J/(mol·K) |
Std enthalpy of (ΔfH⦵298)formation |
−90.65 kJ/mol |
Gibbs free energy (ΔfG⦵)
|
−68.48 kJ/mol |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards
|
extremely strong irritant, highly toxic, highly corrosive |
GHS labelling: | |
Danger | |
H260, H301, H314 | |
P223, P231+P232, P260, P264, P270, P280, P301+P316, P301+P330+P331, P302+P335+P334, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P330, P363, P370+P378, P402+P404, P405, P501 | |
NFPA 704 (fire diamond) | |
200 °C (392 °F; 473 K) | |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
|
77.5 mg/kg (oral, rat)[5] |
LC50 (median concentration)
|
22 mg/m3 (rat, 4 h)[6] |
NIOSH (US health exposure limits): | |
PEL (Permissible)
|
TWA 0.025 mg/m3[4] |
REL (Recommended)
|
TWA 0.025 mg/m3[4] |
IDLH (Immediate danger) |
0.5 mg/m3[4] |
Safety data sheet (SDS) | ICSC 0813 |
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).
|
Lithium hydride is an
Physical properties
LiH is a
The
: 49Synthesis and processing
LiH is produced by treating lithium metal with hydrogen gas:
- 2 Li + H2 → 2 LiH
This reaction is especially rapid at temperatures above 600 °C. Addition of 0.001–0.003% carbon, and/or increasing temperature and/or pressure, increases the yield up to 98% at 2-hour residence time.[3]: 147 However, the reaction proceeds at temperatures as low as 29 °C. The yield is 60% at 99 °C and 85% at 125 °C, and the rate depends significantly on the surface condition of LiH.[3]: 5
Less common ways of LiH synthesis include thermal decomposition of lithium aluminium hydride (200 °C), lithium borohydride (300 °C), n-butyllithium (150 °C), or ethyllithium (120 °C), as well as several reactions involving lithium compounds of low stability and available hydrogen content.[3]: 144–145
Chemical reactions yield LiH in the form of lumped
: 155Bulk cold-pressed LiH parts can be easily machined using standard techniques and tools to
A more energy efficient route to form lithium hydride powder is by
Reactions
LiH powder reacts rapidly with
LiH is highly reactive towards
- LiH + H2O → Li+ + H2 + OH−
LiH is less reactive with water than Li and thus is a much less powerful reducing agent for water,
LiH pellets slowly expand in moist air, forming
: 14LiH reacts with sulfur dioxide to give the dithionite:
- 2 LiH + 2 SO2 → Li2S2O4 + H2
though above 50 °C the product is lithium sulfide instead.[3]: 9
LiH reacts with
- LiH + LiOH → Li2O + H2
Lithium hydride is rather unreactive at moderate temperatures with O2 or Cl2. It is, therefore, used in the synthesis of other useful hydrides,[8] e.g.,
Applications
Hydrogen storage and fuel
With a hydrogen content in proportion to its mass three times that of NaH, LiH has the highest hydrogen content of any hydride. LiH is periodically of interest for hydrogen storage, but applications have been thwarted by its stability to decomposition. Thus removal of H2 requires temperatures above the 700 °C used for its synthesis, such temperatures are expensive to create and maintain. The compound was once tested as a fuel component in a model rocket.[9][10]
Precursor to complex metal hydrides
LiH is not usually a hydride-reducing agent, except in the synthesis of hydrides of certain metalloids. For example, silane is produced in the reaction of lithium hydride and silicon tetrachloride by the Sundermeyer process:
- 4 LiH + SiCl4 → 4 LiCl + SiH4
Lithium hydride is used in the production of a variety of reagents for
In nuclear chemistry and physics
Lithium hydride (LiH) is sometimes a desirable material for the shielding of
Lithium deuteride
Lithium deuteride, in the form of
The corresponding
- 6LiD + n → 4He + T + D
The deuterium and tritium then fuse to produce helium, one neutron, and 17.59 MeV of free energy in the form of gamma rays, kinetic energy, etc. The helium is an inert byproduct.
Before the
Safety
LiH reacts violently with water to give hydrogen gas and LiOH, which is caustic. Consequently, LiH dust can explode in humid air, or even in dry air due to static electricity. At concentrations of 5–55 mg/m3 in air the dust is extremely irritating to the mucous membranes and skin and may cause an allergic reaction. Because of the irritation, LiH is normally rejected rather than accumulated by the body.[3]: 157, 182
Some lithium salts, which can be produced in LiH reactions, are toxic. LiH fire should not be extinguished using carbon dioxide, carbon tetrachloride, or aqueous fire extinguishers; it should be smothered by covering with a metal object or graphite or
References
- ^ ISBN 0-8493-0486-5.
- ISBN 978-0-85404-665-2. Retrieved 1 November 2011.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad Smith, R. L.; Miser, J. W. (1963). Compilation of the properties of lithium hydride. NASA.
- ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0371". National Institute for Occupational Safety and Health (NIOSH).
- ^ Chambers, Michael. "ChemIDplus - 7580-67-8 - SIAPCJWMELPYOE-UHFFFAOYSA-N - Lithium hydride - Similar structures search, synonyms, formulas, resource links, and other chemical information". chem.sis.nlm.nih.gov. Retrieved 10 April 2018.
- ^ "Lithium hydride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ^ Solvent-and catalyst-free mechanochemical synthesis of alkali metal monohydrides IZ Hlova, A Castle, JF Goldston, S Gupta, T Prost… - Journal of Materials Chemistry A, 2016
- ^ "NCERT Chemistry Textbook" (PDF).
- ^ Lex Archived 2008-07-23 at the Wayback Machine. Astronautix.com (1964-04-25). Retrieved on 2011-11-01.
- ^ Empirical laws for hybrid combustion of lithium hydride with fluorine in small rocket engines. Ntrs.nasa.gov. Retrieved on 2011-11-01. (password-protected)
- ISBN 978-1-56347-115-5. Retrieved 2 November 2011.
- .
- ^ Massie, Mark; Dewan, Leslie C. "US 20130083878 A1, April 4, 2013, NUCLEAR REACTORS AND RELATED METHODS AND APPARATUS". U.S. Patent Office. U.S. Government. Retrieved 2 June 2016.