Chemistry - Thermochemistry Question with Solution | TestHub

Lattice enthalpy magnitude is inversely proportional to the sum of ionic radii ($r_{+}+r_{-}$) because all the compared compounds have the same ionic charges ($+1$ and $-1$). CsF consists of the largest alkali metal cation (Cs⁺) and the smallest halide anion (F⁻). Among the given fluorides (LiF, KF, RbF), the smaller cations decrease the interionic distance, resulting in a higher magnitude of lattice enthalpy than CsF. Conversely, in the cesium halides (CsCl, CsBr, CsI), the larger anions increase the distance, lowering the lattice enthalpy. Therefore, exactly 3 compounds (LiF, KF, and RbF) have a greater magnitude of lattice enthalpy than CsF.