How many molecules of Mg3N2 (magnesium nitride) are formed when excess Mg (magnesium) reacts with 24.3 moles of N2 (nitrogen gas)?
3Mg(s) + N2(g) → Mg3N2(s)

Please explain or show how to work it as well!

Explanation:

3Mg(s) + N2(g) = Mg3N2(s)

First check that the equation is balanced. In this case, it is.

Assuming that magnesium is the limiting reactant:

       We find that the atomic mass of magnesium is approximately

       24.3g, so the molecular weight is just 24.3g\mol

    2. Next we need the mole to mole ratio. As there are 3

        magnesiums for 1 magnesium nitride (shown by the coefficients), the                    

        mole to mole ratio is 1 mol Mg3N2\3 mol Mg.

    3. We need the amount of the substance, in grams. Since you have not    

        stated it in the question, I'll just do 10g AS AN EXAMPLE. Note that    

       depending on the amount, the LIMITING REAGENT MAY DIFFER.

   4.  Finally, we need the molecular weight of Mg3N2, which we can easily    

        calculate to be around 100.9\mol.

   5.  Putting this all together, we have 10gMg⋅ (mol Mg\24.3gMg)

        (1mol Mg3N2\ 3mol Mg) (100.9g Mg3N2\mol Mg3N2)

        the units will cancel to leave gMg3N2 (grams of magnesium nitride):

       10gMg ⋅ (mol Mg\24.3gMg) (1mol Mg3N2\3mol Mg)

       (100.9g Mg3N2\mol Mg3N2)

Doing the calculation yields approximately 13.84g.

Assuming that nitrogen is the limiting reactant:

Similarly, following the above steps but with 10g of nitrogen yields 36.04g

In conclusion, as we produce less amount of Mg3N2 when we assumed that Mg was the limiting reagent, magnesium is the limiting reagent and nitrogen is the excess.

Note: This is in THIS CASE, where we have 10g of both. The answer may vary depending on the amount of each substance.

  1.46×10^25 molecules

Explanation:

Each mole of N₂ reacts with 3 moles of Mg to form 1 mole of Mg₃N₂. That is, the number of moles of product is equal to the number of moles of nitrogen gas when excess magnesium is present.

There are 6.022×10²³ molecules in each mole of a substance, so the number of molecules of Mg₃N₂ is

  (24.3 mol)(6.022×10²³ molecules/mol) = 1.46×10²⁵ molecules