So, you have 3 mol of Na. How many moles of Cl2 would you need?

Question

How many moles of Cl2 would you need to add to have stoichiometrically equivalent amount of Na and Cl2?

2Na+Cl2 ---> 2NaCl

Answer 1

3molNa x 1molCl2/2molNa = 1.5 moles Cl2

Answer 2

I'm not sure I completely understand the question, but from what I do understand I did this. Since you're dealing with moles you can easily convert from one mole of a molecule, or compound, to another. That's why chemical equations are so handy!
To start off we look at what we want units our answer should be in. It looks like we want it in moles of Cl2. Since that's a single unit answer we want to start off with a single unit number. In this case, the 3 mol Na is the most logical one we have. And remember, our goal is mol Cl2.
Lastly, I think it might be important for you to understand how we can derive units from the chemical equation. Basically, for any equation the number in front has the unit of moles. For example, our equation can be described as 2 moles of Sodium plus one mole of Chlorine gas gives us 2 moles of Sodium Chloride. With this little tid bit of information we can pluck out a couple of conversion factors. The best one is 2 mol Na : 1 mol Cl2. Now, we can start doing some stoichiometry.
First, start off with the single unit and use the conversion factor to convert it to mol Cl2.
3 mol Na / 2 mol Na * mol Cl2 = 1.5 mol Cl2
Now, this is where I get a little confused. If we follow the significant figures then we should round our answer up to 2. But your question asks for the equivalent of Na and Cl2, which, in my mind anyway, means that they want a whole number for NaCl. And if we use the proper sig figs then we'll have one chloride atom. So, the best thing I think to do is to leave it as 1.5. It makes sense to me, since it takes 2 Na^+ and 2 Cl^- atoms to create 2 NaCl. And since we have an odd number we need to split a chlorine gas molecule to get Just one chlorine atom.

I hope that ansers your question,
S S