how do you calculate the number of molecules in 40g of N2 and 40g of O2?

Answer 1

That's probably a mol conversion.
You'll need to remember that 1 mol of any atom or molecule weighs as many grams as it's atomic weight.

1 atom of Oxygen is 16 amu, so O2 is 32 amu.
Therefore 1 mol of O2 is 32 grams.

Now to figure out the problem, you'll have to set up the problem the way you learned ( I learned parenthesis), so set it up as:

1 mol 02 / 32 grams

and so forth.
Hope his helps.

Answer 2

MW O2 = 32 g/mole, 40g O2 => 1.25 moles
MW N2 = 28 g/mole, 40g N2 => 1.43 moles

there are 6.023*10^23 molecules/mole

so 1.25 moles O2 has 1.25 moles*(6.023*10^23molecules/mole)
= 7.52 * 10^23 molecules

molecule N2 = 8.61*10^23 molecules

Answer 3

calculate the moles of the 40g of N2, then ,multiply per the number of Avogadro.

Do the same with the oxygen.