How many liters of H₂ is required to obtain 72g of H₂O?

Given:
m (H2O) = 72 g

To find:
V (H2) -?

Solution:
1) Write the reaction equation:
2H2 + O2 => 2H2O;
2) Calculate the molar mass of H2O:
M (H2O) = Mr (H2O) = Ar (H) * N (H) + Ar (O) * N (O) = 1 * 2 + 16 * 1 = 18 g / mol;
3) Calculate the amount of substance H2O:
n (H2O) = m (H2O) / M (H2O) = 72/18 = 4 mol;
4) Determine the amount of substance H2:
n (H2) = n (H2O) = 4 mol;
5) Calculate the volume of H2 (under normal conditions):
V (H2) = n (H2) * Vm = 4 * 22.4 = 89.6 liters.

Answer: The volume of H2 is 89.6 liters.