What mass of potassium will react with 8 g of hydrogen?

Based on the task data, we write down the process equation:
2K + H2 = 2KH – OBP, potassium hydride is released;

Calculations according to the formulas of substances:
M (K) = 39.1 g / mol;

M (H2) = 2 g / mol;

Y (H2) = m / M = 8/2 = 4 mol.

Proportion:
4 mol (H2) –X mol (K);

-1 mol -2 mol from here, X mol (K) = 4 * 2/1 = 8 mol.

Find the mass of the metal:
m (K) = Y * M = 8 * 39.1 = 312.8 g

Answer: you need potassium weighing 312.8 g