Help! how to calculate volume? (1 Viewer)

[fabl]

Methane gas, CH4
t readily burns in air to
produce carbon dioxide and water vapour. If all gas
volumes are measured at STP calculate:
(a) the volume of oxygen gas which is required for
the complete combustion of 12.5 L of methane
gas
(b) the volume of air required for reaction, given
that air contains 20% oxygen.

 

[InteGrand]

Methane gas, CH4
t readily burns in air to
produce carbon dioxide and water vapour. If all gas
volumes are measured at STP calculate:
(a) the volume of oxygen gas which is required for
the complete combustion of 12.5 L of methane
gas
(b) the volume of air required for reaction, given
that air contains 20% oxygen.

The balanced combustion chemical equation is .

(a) The above equation shows that for complete combustion, we need twice the moles of oxygen gas as that of methane. By Avogadro's Law (equal volumes of gases have equal number of moles), this means that we also need twice the volume of oxygen gas as methane, so the volume of oxygen gas required is .

(b) We still need 25 L of oxygen gas, but air contains only 20% (i.e. one-fifth) oxygen, so we need five times the previous answer of air, i.e. we need 125 L of air.