How many molecules are present in 1.0 kg of hydrogen gas (H2)?

To determine the number of molecules present in 1.0 kg of hydrogen gas (H2), we start by converting the mass of hydrogen into moles, which can then be converted into molecules using Avogadro's number.

First, we need to find the molar mass of hydrogen gas. The atomic mass of a hydrogen atom is approximately 1 g/mol. Since H2 consists of two hydrogen atoms, the molar mass of H2 is roughly 2 g/mol.

Next, we convert the mass of hydrogen gas from kilograms to grams. Since 1 kg is equal to 1000 grams, we have:

1.0 kg of H2 = 1000 g of H2.

Now, we can calculate the number of moles of H2 in 1000 g by using the formula:

Number of moles = Mass (g) / Molar mass (g/mol).

Substituting the known values:

Number of moles = 1000 g / 2 g/mol = 500 moles of H2.

Next, to find the number of molecules, we multiply the number of moles by Avogadro's number, which is approximately 6.02 x 10^23 molecules/mol: