i really need help...(please explain it!)?

Question

What volume of HCN(g) can be obtained from 70.0 L CH4(g), 70.0 L NH3(g), and 70.0 L O2(g)? The volumes of all gases are measured at the same temperature and pressure.

The Chemical Formula is
2CH4(g) +2NH3(g) + 3O2---->2HCN+ 6H2O

Answer 1

Since the volumes of all gases are measured at the same temperature and pressure, the volumes of all gases are proportional to the moles of the gases. The chemical formula indicates that 2 moles of CH4 reacts with 2 moles of NH3 reacts with THREE moles of O2. Hence O2 is the limiting reagent. The maximum volume (at the same temperature and pressure) of HCN(g) can be obtained is: 70.0*2/3 L = 46.7 L.