Since 1891 lighting lamps have been manufactured in the Netherlands. The improvement today in comparison to 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.