What mass of hydrogen must be taken to obtain 20 g of hydrogen chloride from chlorine?

To solve the problem, you need to write the equation:
H2 + Cl2 = 2HCl – reaction of the compound, hydrogen chloride was obtained;
Let’s calculate the molar masses of substances:
M (HCl) = 36.5 g / mol;
M (H2) = 2 g / mol.
Let us determine the amount of moles of hydrogen chloride, if the mass is known:
Y (HCl) = m / M = 20 / 36.5 = 0.5 mol.
We make the proportion:
0.5 mol (HCl) – X mol (H2);
-2 mol -1 mol hence, X mol (H2) = 0.5 * 1/2 = 0.25 mol.
Find the mass of hydrogen:
m (H2) = Y * M = 0.25 * 2 = 0.5 g.
Answer: the mass of hydrogen is 0.5 g.