Igesi ejwayelekile isho igesi evumelana ne-adeal gas state equation (PV=nRT) ngaphansi kwezimo ezijwayelekile (ingcindezi evamile nezinga lokushisa, okungukuthi 1 atm kanye no-273.15K). Igesi ejwayelekile yigama embonini yegesi. Izinto ezijwayelekile zingamazinga okulinganisa anokugxila okufanayo, ukuzinza okuhle kanye nenani elinembile. Zinemisebenzi eyisisekelo yokukhiqiza kabusha, ukulondoloza nokudlulisa amanani. Asetshenziswa emikhakheni yokulinganisa ngokomzimba, kwamakhemikhali, kwebhayoloji kanye nobunjiniyela ukuze kulinganiswe amathuluzi okulinganisa nezinqubo zokulinganisa,