Which reagent is limiting: 5 g of Zn with 10 g of HCl?

Answer

The zinc is limiting — the HCl is in excess.

Explanation

Step 1 — Write the balanced equation

Zn + 2 HCl → ZnCl₂ + H₂

The ratio that matters is 1 mol Zn to 2 mol HCl. Grams cannot be compared directly.

Step 2 — Convert both masses to moles

reagent	mass	molar mass	moles
Zn	5 g	65.38 g/mol	0.0765 mol
HCl	10 g	36.46 g/mol	0.274 mol

Step 3 — Compare against the mole ratio

The 0.0765 mol of zinc would consume:

0.0765 mol × 2 = 0.153 mol HCl

There is 0.274 mol of HCl available, which is more than enough. Run it the other way and the 0.274 mol of acid would need 0.137 mol of zinc — nearly twice what is present.

Step 4 — State the conclusion

Zinc runs out first, so zinc is the limiting reagent and it is the zinc that fixes how much hydrogen can be produced:

n(H₂) = n(Zn) = 0.0765 mol → about 0.15 g of H₂

Check

There are twice as many grams of acid, but that is not the test. The comparison has to be made in moles against the coefficients of the balanced equation.