A furnace that provides heat by burning methane gas must have the correct mixture of air and fuel to operate efficiently. What is the mole ratio of air to methane gas in the combustion of methane? Hint: Air is 20% oxygen.

Answer 1

CH4 + 2O2 ==> CO2 + 2H2O
So 1L CH4 requires 2 L pure O2.
Since air is only 20% O2 (that's 1/5), then 1L CH4 requires 5*2 = 10L air.
Try it in reverse. 10L air x 0.2 = 2 moles pure O2.
mole ratio air/methane = 10/1