Calculate the volume of hydrogen released when interacting with water, potassium with a mass of 7.8 g.

2K + 2H2O = 2KOH + H2

According to the condition of the problem, the mass of potassium is 7.8 g, water is in excess.

Let’s calculate the amount of potassium substance.

n (K) = m / M = 7.8 / 39 = 0.2 mol

According to the reaction equation: from 2 moles of potassium, 1 mole of hydrogen is obtained. This means that from 0.2 mol of potassium should be obtained at 100% yield of 0.1 mol of hydrogen.

n (H2) = 0.1 mol

To calculate the volume of hydrogen, you need to multiply the number of moles of hydrogen by the molar volume Vm.

Vm = 22.4 liters under normal conditions (0 ° C, 1 atmosphere).

V (H2) = n * Vm = 0.1 * 22.4 = 2.24 l (n.u.).