Although sodium is less reactive than potassium, this process works because at such high temperatures potassium is more volatile than sodium and can easily be distilled off, so that the equilibrium shifts towards the right to produce more potassium gas and proceeds almost to completion.
ɔːlðˈoʊ sˈoʊdiəm ɪz lˈɛs ɹɪˈæktɪv ðɐn pətˈæsiəm, ðɪs pɹˈɑːsɛs wˈɜːks bɪkˈʌz æt sˈʌtʃ hˈaɪ tˈɛmpɹɪtʃɚz pətˈæsiəm ɪz mˈoːɹ vˈɑːlɐɾəl ðɐn sˈoʊdiəm ænd kæn ˈiːzili biː dɪstˈɪld ˈɔf, sˌoʊ ðætðɪ ˌiːkwɪlˈɪbɹiəm ʃˈɪfts təwˈɔːɹdz ðə ɹˈaɪt tə pɹədˈuːs mˈoːɹ pətˈæsiəm ɡˈæs ænd pɹˈoʊsiːdz ˈɔːlmoʊst tə kəmplˈiːʃən.