Lithium bromide (LiBr), also known as lithium monobromide, is a compound of the elements lithium and bromine, having one atom of lithium bonded to one atom of bromine. It is an ionic compound, meaning that the lithium atom “gives” one electron to the bromine atom, with the result that the lithium atom becomes positively charged and the bromine atom negatively charged; the atoms are then bonded together by electrostatic attraction. Ionic bonding is a common feature of simple metal/non-metal compounds. Lithium is a metal belonging to a group of elements known as the alkali metals because they react with water to produce strong alkalis. Bromine belongs to a group of reactive non-metallic elements known as the halogens, which also include fluorine, chlorine and iodine.
The compound can also be described as a salt, that is, a substance that can be made by the reaction of a base and an acid — in this case, lithium hydroxide (LiOH) and hydrobromic acid (HBr): LiOH + HBr -> LiBr + H2O. Common salt, or sodium chloride, is another example. Normally, however, lithium bromide is manufactured by reacting hydrobromic acid with lithium carbonate. Lithium bromide is very soluble in water and forms hydrates, which are compounds that include water. It also is extremely hygroscopic, which means that it absorbs moisture from the air, and because of this, it is widely used as a desiccant or drying agent in dehumidifiers, industrial drying systems and air conditioning systems.
The biggest commercial and industrial use of lithium bromide is in refrigeration units where water is used as a coolant; these are suitable for applications where freezing is not required, such as chillers and air conditioning systems. Cooling is achieved by evaporation, a process that absorbs heat from the surroundings, just like the way sweating keeps the body cool. To maintain the cooling effect, the water that has evaporated must be recovered from the resulting moist air, and this is achieved by spraying it with a strong solution of lithium bromide that absorbs the water vapor, leaving a more dilute solution. This solution is heated in a boiler to drive off excess water, creating a stronger solution; both the water, converted back to liquid in a condenser, and the strong lithium bromide solution are recycled through the system.
Lithium compounds affect central nervous system (CNS) functions and have been used to treat certain mental conditions, especially bipolar disorder. In modern times, lithium carbonate is normally prescribed, but lithium bromide has been used in the past for the treatment of epilepsy. Ingestion of lithium compounds can produce serious toxic effects because of their action on the CNS.