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.
Conclusion in relation to the previous answers. was adding CsBr a good idea ? Mark the correct answer.
`implies` Adding CsBr is counterproductive.
`implies` Adding CsBr has no influence
`implies` Adding CsBr is advantageous
`implies` From these data no clear answer can be given.

Answer

`(CeBr_(3))_("glucose") overset(-H_(1))rarr Ce^(3-) + 3Br^(-)`
`Ce^(3+) + 3 Br overset(-He)rarr (CeBr_(3))_("molecules")
___________ `(CeBr_(3))_("tattice") overset(+H_(3)) rarr (CeBr_(3))_("molecules") " "H_(3) =- H_91) + H_(e)`
The lattice energy of the solid cn be calculated using the Boron - Lande formula:
`H_(1) = d(Z_(+)Z_(-)Ae^(2))/(r_(+)+R_(-))(1-(1)/(n))`
The factor `Fe_(2)` (necessary in order to calculate the lattice energy in KJ `"mol"^(-1)` ) amounts of 139 when the ionic radii are substituted in nm . The Madelung constant A for the lattice is 2.985. The Born exponent n is 11 . The charge of the ions `Z_(+)` and `Z_(-)` are integer number (Z is negative) . For the calculation of the energy of gaseous `CeBr_(3)` (when formed from ions ) the same Born-Londe formula can be used without A. The structure of `CeBr_(3)` in the gas phase is planar triangular . The radius of `Ce^(3+)` is 0.115 nm and of Br is 0.182 nm.