Question

What mass of hydrogen gas is produced when 3.0 mol of iron react with excess hydrochloric acid according to the reaction below

2Fe + 6HCl --> 2FeCl3 + 3H2

Answer 1

We compare the moles of H2 with Fe if 2 moles of Fe gives 3 moles of H2 so 3 moles of Fe would give 4.5 moles of H2. Now by Formula
N of moles=Mass/molar mass
molar mass of H2 is 2 and moles is 4.5
we multiply these values to get mass
2*4.5=9
9g of H2 is produced :)