The answer is :
HCl is the limiting reactant and 6.75 mol can be formed.
The explanation:
1- we need to get the balanced reaction equation:
Mg + 2HCl --------> MgCl2 + H2
Here, you can see from the balanced chemical equation, that 1 mol Mg reacts with 2 mol HCl.
2-by using stoichiometry for each reactant:
So, 8 mol Mg should react with 2* 8 mol HCl
So, 8 mol Mg should react with 16 mol HCl
But the given amount of HCl is 13.5 mol, which is less than the required (16 mol) to react completely with Mg.
-now Amount of HCl is less So, HCl is the LIMITING REAGENT.
-when limiting reagent (or limiting reactant, LR) in a chemical reaction is the substance that is totally consumed when the chemical reaction is complete. The amount of product formed is limited by this reagent.
Also, you can see that 2 mol HCl corresponds to the formation of 1 mol H2.
SO, 1 mol HCl corresponds to the formation of 1/2 mol H2.
1 mol HCl → 1/2 mol H2
13.5 mol HCl → ????
13.5 mol HCl corresponds to the formation of (1/2)*13.5 mol H2 = 6.75 mol H2.
So, HCl is the limiting reactant, and 6.75 mol H2 can be formed