Question

Over the years, the thermite reaction has been used for welding railroad rails, in incendiary bombs, and to ignite solid fuel rocket motors.

Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s)

What mass (in g) of aluminum must be used to produce 15.0 g iron?

Answer 1

molar mass of Fe = 55.8 g/mol
number of mol of Fe = (given mass)/(molar mass)
= 15.0/55.8
= 0.269 mol

reaction taking place
Fe2O3(s) + 2Al(s) --> 2Fe(l) + Al2O3(s)

according to reaction
2 mol of Fe is produced by 2 mol of Al
1 mol of Fe is produced by 1 mol of Al
0.269 mol of Fe is produced by 0.269 mol of Al
so,
number of mol of Al = 0.269 mol

molar mass of Al = 27.0 g/mol
mass of Al required = (number of mol of Al)*(molar mass of Al)
= 0.269*27.0
= 7.26 g

Answer: 7.26 g