delta_Tf = i * Kf * m. Kf = molal cryoscopic constant = RTf^2M_solvent/(1000*delta_H_fus). For water: Kf = 1.86 K.kg/mol, Tf = 273 K. Physical explanation: solute particles interfere with crystal lattice formation, requiring a lower temperature for freezing. delta_Tf is always positive (freezing point drops). Applications: antifreeze (ethylene glycol in car radiators), salting icy roads (NaCl lowers freezing point). Kf > Kb for water because delta_H_fus < delta_H_vap (less energy involved in fusion, so the effect per particle is larger). Camphor is the best solvent for cryoscopy (Kf = 40 K.kg/mol, very high sensitivity). Molar mass formula: M = (i * Kf * w_solute * 1000) / (delta_Tf * w_solvent).