дано
m(P) = 15.5 g
m(O2)-?
4P+5O2-->2P2O5
M(P) = 31 g/mol
n(P) = m/M = 15.5 / 31 = 0.5 mol
4n(P) = 5n(O2)
n(O2) = 5*0.5 / 4 = 0.625 mol
M(O2) =32 g/mol
m(O2) = n*M = 0.625 * 32 = 20 g
ответ 20 г
