дано
m(H2O) = 7.2 g
V(O2)-?
2H2O-->2H2+O2
M(H2O) = 18 g/mol
n(H2O) = m/M =7.2 / 18 =0.4 mol
2n(H2O) = n(O2)
n(O2) = 0.4/ 2 = 0.2 mol
V(O2) = n(O2)*Vm = 0.2 * 22.4 = 4.48 L
ответ 4.48 л
