How many molecules are present in 25 grams of NH3?

To determine how many molecules are present in 25 grams of NH3 (ammonia), we first need to calculate the number of moles in that mass of the compound.

The molecular weight of NH3 can be calculated as follows:

• Nitrogen (N) has an atomic mass of approximately 14.01 g/mol.

• Each hydrogen (H) atom has an atomic mass of about 1.01 g/mol, and there are three hydrogen atoms in NH3.

Therefore, the molecular weight of NH3 is:

14.01 g/mol (for nitrogen) + 3 x 1.01 g/mol (for hydrogen) = 17.04 g/mol.

Next, we use the formula to find the number of moles:

Number of moles = mass (g) / molecular weight (g/mol).

Substituting the values we have:

Number of moles = 25 g / 17.04 g/mol ≈ 1.47 moles.

Next, to find the number of molecules, we apply Avogadro's number, which is approximately 6.022 x 10^23 molecules per mole.

Multiplying the number of moles by Avogadro’s number gives:

1