Question

What is the theoretical yield of hydrogen gas if 5.00 mol of zinc are added to an excess of hydrochloric acid?

Answer 1

So in this problem, your limiting reactant is the 5.00 mol of Zn, because you have an excess of hydrochloric acid.

The first step to answering this problem is to set up a balanced equation.
You start with Zn + HCl ⇒ ZnCl +H
In order to balance it, you have to know that Zinc is a +2 ion, Cl is a -1 ion, and H is a +1 ion. Each molecule must be balanced (meaning ionic charges equal to zero),  as well as the number of each element on either side of the reaction.
This gives you Zn + 2HCl ⇒ ZnCl₂ + 2H
Now, in order to find how much Hydrogen gas you have, you have to know how many atoms of Zn you have.
1 mol is 6.022 × 10²⁴ atoms (Avogadro's Number), so if you have 5 mol of Zn, you have 3.011 × 10²⁵ atoms of zinc.
Plug this into the reaction and re-balance the formula.
(3.011 × 10²⁵ Zn) + (6.022 × 10²⁵ HCl) ⇒ (3.011 × 10²⁵ ZnCl₂) +
(6.022 × 10²⁵ H)

You end up with (6.022 × 10²⁵ H), or 10.00 mol H (g)

Answer 2

the theoretical  yield   of  hydrogen gas is  10 g

   calculation

Step 1: write the equation for reaction

Zn + 2 HCl →  zncl₂  + H₂

Step 2: use the mole ratio to find the moles of H₂

from equation above Zn : H₂  is 1: 1 therefore the  moles of H₂ = 5.00 moles

Step 3: find the theoretical yield(mass) for H₂

mass = moles  × molar mass

from periodic table the molar mass of H₂= 1×2  = 2 g/mol

mass  =  5  moles  × 2 g/mol  = 10 grams