When 0.010 moles of Zn(s) reacts with 30.0 mL of 1.0 M HCl, the H2 gas produced is collected in a 1.0 L flask at a temperature of 270 K. What is the pressure (atm) of H2 gas collected?

Question

Zn(s) + 2HCl(aq) = ZnCl2(aq) + H2(g)

Answer 1

This is a limiting reagent (LR) problem.
mols Zn = 0.01
mols HCl = M x L = 0.03 x 1 = 0.03

mols H2 produced from Zn if we had all of the HCl we needed = 0.01 (from the 1 mol Zn gives 1 mol H2.

molsl H2 produced from 0.03 mols HCl if we had all of the Zn we needed = 0.03 x 1/2 = 0.015 mols H2 (from 2 mol HCl produces 1 mol H2).
In LR problems the SMALLER amount of the product produces is the correct answer (0.01 mol) and the reagent producing that value is the LR.
So 0.01 mol H2 produced. Substitute that into PV = nRT and solve for P.