In a very violent reaction called a thermite reaction, aluminum metal reacts with iron (iii) oxide to form iron metal and aluminum oxide according to the following equation:

Here's the equation:
Fe2 O3 + 2Al → 2Fe + Al2 O3 

Here's the question.
What mass of Al will react with 150g of Fe2 O3? 

In every 2 moles Al you need 1 mole Fe2O3 

moles = mass / molar mass 
moles Fe2O3 = 150 g / 159.69 g/mol 
= 0.9393 moles 

moles Al needed = 2 x moles Fe2O3 
= 2 x 0.9393 mol 
= 1.879 moles Al needed 

mass = molar mass x moles 
mass Al = 26.98 g/mol x 1.879 mol 
= 50.69 g 
= 51 g (2 sig figs) 

So the mass of Al that will react with 150g of Fe2 O3 is 51 grams.