Calculate the mass of hydrogen obtained by reacting 14 g of lithium with hydrochloric acid.

Decision:
1. Let’s compose the reaction equation:
2Li + 2HCl = H2 + 2LiCl – substitution reaction, hydrogen gas and lithium chloride are released;
2. Determine the amount of mol of lithium, if the mass is known:
M (Li) = 6.93 g / mol;
Y (Li) = m (Li) / M (Li);
Y (Li) = 14 / 6.93 = 2.02 mol;
3. Let’s make a proportion according to the reaction equation:
2.02 mol (Li) – x mol (H2);
-2 mol             – 1 mol from here, X mol (H2) = 2.02 * 1/2 = 1.01 mol;
4. Let’s calculate the mass of hydrogen:
M (H2) = 2 g / mol;
m (H2) = Y (H2) * M (H2); m (H2) = 1.01 * 2 = 2.02 g.
Answer: during the reaction, hydrogen is released weighing 2.02 g.