How do I write Balanced chemical equations?

Na + Cl2 ---> NaCl

balance the Cl:

Na + Cl2 ---> 2NaCl

balance the Na:

2Na + Cl2 ---> 2NaCl

I discuss equation balancing here:

http://chemteam.info/Equations/Equations.html

Best wishes on the test.

Look at the charges, and write mole quantities based on your charges so that they will balance.

For your example, you have Chlorine gas, Cl2, and it is reacting with Sodium, Na. Cl has a charge of -1, and you have 2 of them, so you have a sum of -2 for the Chlorine part. Na has a charge of +1, so you need 2 Sodiums to equal the -2 from the Chlorine part. So, your final balanced reaction would be 2Na + Cl2 2NaCl.

if you look at the table of elements, the halogens(flourine and down) all have a charge of -1, the family to the left of that has a charge of -2, and the one to the left of that has a charge of -3. As for positive ions, family one has a charge of one and two a charge of two. For a compound to form, the charges have to cancel. such as: potassium reacts with Iodine, there will be one K and one I, and so forth. When balancing an equation, determine that part first and write those amounts as subscripts. Then, to be balanced, the equation has to have the same number of molecules of each element on either side of the equation. Put a coefficient number in front of the chemical symbol to indicate how many molecules there are, but this has to match up with the other side.