(ot grech. baros - tyazhest' i tropos - napravlenie, povorot, o6paz, harakter).

Sostoit v tom, chto v dvuh- i mnogokomponentnyh sistemah "zhidkost'-zhidkost'" ili "zhidkost'-gaz" pri bol'shih davleniyah i opredelennyh temperaturah v pole tyagoteniya sosushestvuyushie fazy menyayutsya mestami: nahodyashayasya sverhu, menee plotnaya pri obychnyh usloviyah faza stanovitsya tyazheloi i opuskaetsya vniz. Barotropnoe yavlenie vyzyvaetsya razlichiem szhimaemosti komponentov i pereraspredeleniem koncentracii v granichashih fazah; pri uvelichenii davleniya faza, soderzhashaya komponent s bol'shei molekulyarnoi massoi, stanovitsya tyazhelee i tonet v drugoi faze.
Vpervye barotropnoe yavlenie nablyudal X. Kamerling-Onnes (N. Kamerlinghi-Onnes) v sisteme vodorod (zhidkost')- gelii (gaz): pri temperature 20,1 K i davlenii 49 atm gazovaya faza opuskalas' pod zhidkuyu. Barotropnoe yavlenie obnaruzheno v sistemah "ammiak-azot" (pri temperature 180 K i davlenii 1800 atm), "ammiak-azot-vodorod" (pri davlenii 3500-3700 atm i temperature 170 K), v trehfaznyh sistemah s dvumya zhidkimi i odnoi gazovoi fazami ("metanol-toluol", "aceton-anilin") i dr.