As a result of the reaction between hydrogen and oxygen, water was formed

As a result of the reaction between hydrogen and oxygen, water was formed with a volume of 18 cm3 (P (H2O) = 1 g / cm3). Find the masses of the gases that have reacted.

Given:
V (H2O) = 18 cm ^ 3
ρ (H2O) = 1 g / cm3

To find:
V (H2) -?
V (O2) -?

Solution:
1) Write the reaction equation:
2H2 + O2 => 2H2O;

2) Find the mass of H2O:
m (H2O) = ρ (H2O) * V (H2O) = 1 * 18 = 18 g;

3) Find the amount of substance H2O:
n (H2O) = m (H2O) / Mr (H2O) = 18/18 = 1 mol;

4) Find the amount of substance H2 and O2 (taking into account the reaction equation):
n (H2) = n (H2O) = 1 mol;
n (O2) = n (H2O) / 2 = 1/2 = 0.5 mol;

5) Find the volume of H2 and O2:
V (H2) = n (H2) * Vm = 1 * 22.4 = 22.4 L;
V (O2) = n (O2) * Vm = 0.5 * 22.4 = 11.2 liters.

Answer: The volumes of H2 and O2 are 22.4 liters and 11.2 liters, respectively.