Answer to Question #289172 in General Chemistry for Rookie

Question

Over the years, the thermite reaction has been used for welding railroad rails, in incendiary bombs, and to ignite solid-fuel rocket motors. The reaction is: Fe2O3 + Al → Fe + Al2O3

If there are 798.2 g of Fe2O3 and 797.5 g of Al

a. Which is the limiting reactant? Which is the excess?

b. How much iron is produced in the reaction?

Can you give the steps too

Answer 1

Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) ... balanced equation

Note the mole ratio of iron oxide Fe2O3(s) to iron (Fe) is 1 : 2. Use this and dimensional analysis...

76.73 g Fe x 1 mol Fe/55.85 g x 1 mol Fe2O3/2 mol Fe x 159.69 g Fe2O3/mol Fe2O3 = 109.7 g Fe2O3

Now note the mole ratio of Al to Fe is 2 : 2 or 1 : 1. Use dimensional analysis again...

76.72 g Fe x 1 mol Fe/55.85 g x 2 mol Al/2 mol Fe x 26.98 g Al/mol Al = 37.06 g of Al

Mole ratio of Al2O3 to Fe is 1 : 2.

76.75 g Fe x 1 mol Fe/55.85 g x 1 mol Al2O3/2 mol Fe x 101.96 g Al2O3/mol Al2O3 = 70.06 g Al2O3