if 4.5 g of Zn reacts with 5.0 g of HCl which is the limiting reactant
Zn + 2HCl --> ZnCl2 + H2
mols Zn = grams/atomic mass = 4.5 /65.4 = approx 0.07
mols HCl = 5.0/36.5 = approx 0.14
Now change mols Zn and HCl to mols ZnCl2 or H2 formed. You do this by using the coefficients in the balanced equation.
0.07 mols Zn x (1 mol ZnCl2/1 mol Zn) = approx 0.07 mols ZnCl2.
0.14 mols HCl x (1 mol ZnCl2/2 mols Hcl) = approx 0.07 mols ZnCl2.
These numbers are so close that you must redo them more accurately. The one producing the smaller number of mols ZnCl2 will be the limiting reagent.
To determine the limiting reactant in a chemical reaction, you need to compare the amount of each reactant to their respective stoichiometric coefficients.
The balanced chemical equation for the reaction between zinc (Zn) and hydrochloric acid (HCl) is:
Zn + 2HCl → ZnCl2 + H2
Based on this equation, we can see that 1 mole of Zn reacts with 2 moles of HCl.
To find the moles of each reactant, we need to use their respective molar masses. The molar mass of Zn is approximately 65.38 g/mol, and the molar mass of HCl is approximately 36.46 g/mol.
Calculating the number of moles for each reactant:
Moles of Zn = Mass of Zn / Molar mass of Zn
Moles of Zn = 4.5 g / 65.38 g/mol
Moles of Zn = 0.0688 mol
Moles of HCl = Mass of HCl / Molar mass of HCl
Moles of HCl = 5.0 g / 36.46 g/mol
Moles of HCl = 0.137 mol
Now, to determine the limiting reactant, we compare the moles of each reactant to their stoichiometric coefficients.
From the balanced equation, we see that 1 mole of Zn reacts with 2 moles of HCl. Therefore, for every 1 mole of Zn, we need 2 moles of HCl.
Considering this stoichiometry, we can determine that for the given reaction, we need 2 times the amount of moles of HCl compared to Zn.
Since we have 0.137 moles of HCl, it is more than 2 times the amount of moles of Zn (0.0688 moles), the limiting reactant is Zn.
Therefore, Zn is the limiting reactant in this reaction.