Since 1891 lighting lamps have been manufactured in the Netherlands. The improvement today in comparisonto the first lamp is enormous , especially with the intorduction of the gas discharge lamps. The life- time has increased by orders of magnitude . the colour is also an important aspect. Rare earth metal compunds like CeBr_(3) are now included to reach a colour temperature of 6000K in the lamp the compounds are ionic solids at room temperature , and upon heating they sublime partially to give a vapour of neutral metal halide molecules . To achieve a high vapour pressure, the sublimation enthalpy should be as low as possible. Calculate the enthalpy of sublimation of CeBr_(3) (in intergers, be aware of signs). Attemps to make a better lamp have been undertaken by adding a stoichiometric amount of CsBr to the CeBr_(3) in the lamp leading at room temperature to solid CsCeBr_(4) lattice has a NaCl structure with Cs as cations and tetrahedral CeBr_(4)^(-) as complex anions. Sublimation of CsCeBr_(4) leads to a vapour of CsBr and CeBr_(3) molecules.