How many moles of methanol must react with excess oxygen to produce 5.0 L of carbon dioxide at STP?
The equation for the combustion of methanol is:
Firstly you need to work out how many moles of carbon dioxide are in 5 litres at STP. If you assume that it is an idea gas (it isn't, but it's close enough for this sort of purpose) then 1 mole at STP occupies 22.4 litres. Therefore, at STP 5 litres is
Looking at the equation, it tells you that 2 moles of carbon dioxide are produced by complete combustion of 2 moles of methanol. Therefore, if you have 0.223 moles of carbon dioxide, you would need 0.223 moles of methanol.
Molar mass of methanol is 32.04 g/mol so you would need 0.223 x 32.04 = 7.14 g of methanol.