Aluminum reacts with `H_2SO_4` to form `Al_2(SO_4)_3` . The equation of the chemical reaction is:

`2Al + 3H_2SO_4 -> Al_2(SO_4)_3 + 3H_2 `

2 moles of aluminum react with 3 moles of hydrogen sulfide. 18 moles of Al will react with (18/2)*3 = 27 moles of hydrogen sulfide.

18 moles of aluminum react with 27 moles of hydrogen sulfide in the reaction involving the two.

First we will need to the complete chemical reaction involving sulfuric acid and alluminium.

2Al + 3H2SO4 -----> Al2(SO4)3 + 3H2

From the reaction 

2 moles of Al react with 3 moles of H2SO4 [ That is is 2:3 ratio]

So

18 moles of Al will react with 27 moles of H2SO4.

SOLUTION:-

(18 * 3)/2  = 27 moles of H2SO4.

Therefore 18 moles of Al will require 27 moles of H2SO4 to react.