The metal reacts with the water first, breaking the hydrogen bonds in the water and producing hydrogen gas; this takes place faster for the more reactive heavier alkali metals.
ðə mˈɛɾəl ɹɪˈækts wɪððə wˈɔːɾɚ fˈɜːst, bɹˈeɪkɪŋ ðə hˈaɪdɹədʒən bˈɑːndz ɪnðə wˈɔːɾɚ ænd pɹədˈuːsɪŋ hˈaɪdɹədʒən ɡˈæs; ðɪs tˈeɪks plˈeɪs fˈæstɚ fɚðə mˈoːɹ ɹɪˈæktɪv hˈɛviɚɹ ˈælkəlˌaɪ mˈɛɾəlz.