Question

How many moles of carbon monoxide are needed to react completely with 139kg of Fe2O3.

Answer 1

The balanced equation is Fe2O3 + 3CO = 2Fe + 3CO2. You need this to see the mole to mole ratio for Fe2O3 and CO. Given 139 kg= 139000 g and knowing carbon monoxide's molar mass is 44.01 g/mol and Fe2O3's is 159.69 g/mol, set up the equation like this:
139000 g (1 mol Fe2O3/159.69 g) (3 mol CO/1 mol Fe2O3) (44.01 g/1 mol CO) = 1.15 x10^5 mol CO which makes sense because you have a large amount of Fe2O3