To calculate the number of molecules in a given amount of a substance, we need to know the molar mass of the substance and use Avogadro's number.
Given:
Amount of nitrogen dioxide (NO2) = 78.54 g
To determine the number of molecules, we'll follow these steps:
Calculate the number of moles of nitrogen dioxide:
Number of moles = Mass / Molar mass
The molar mass of nitrogen dioxide (NO2) can be calculated as follows:
Molar mass of NO2 = (Molar mass of N) + 2 × (Molar mass of O)
The molar masses are:
Molar mass of N = 14.01 g/mol
Molar mass of O = 16.00 g/mol
Molar mass of NO2 = 14.01 g/mol + 2 × 16.00 g/mol = 46.01 g/mol
Plugging in the values, we have:
Number of moles = 78.54 g / 46.01 g/mol
Calculate the number of molecules:
Number of molecules = Number of moles × Avogadro's number
Avogadro's number = 6.022 × 10^23 molecules/mol
Plugging in the values, we have:
Number of molecules = Number of moles × Avogadro's number
Now, let's calculate:
Number of moles = 78.54 g / 46.01 g/mol ≈ 1.7078 mol
Number of molecules = 1.7078 mol × 6.022 × 10^23 molecules/mol
Number of molecules ≈ 1.028 × 10^24 molecules
Therefore, approximately 1.028 × 10^24 molecules are present in 78.54 grams of nitrogen dioxide (NO2).