ðɪ ˌaɪsəðˈɜːməlˌaɪsəbˈæɹɪk ɑːnsˈɑːmbəl sˈæɾɪsfˌaɪz sˌoʊ ɪts kˌæɹɪktɚɹˈɪstɪk fˈʌŋkʃən ɪz ðə ɡˈɪbz fɹˈiː ˈɛnɚdʒi .
The isothermal-isobaric ensemble satisfies  so its characteristic function is the Gibbs free energy .