I really don't understand how to change word equations to number equations. For example: Sodium phosphate and calcium chloride react to form calcium phosphate and sodium chloride. In this equation I have no idea how you can find out the subscripts of each element.

Lets start with the easier compounds first. Calcium chloride; calcium is in the second group on the periodic table so it has a charge of +2, chloride is in the 7th group so it has a charge of -1. The overall charge of the molecule is 0 so you need 1 Calcium and 2 Chloride's so you get CaCl2. Sodium chloride; sodium is in the first group so it has a charge of +1 so you need one of each to get an overall charge of 0 and you get NaCl.

For the phosphate molecules, you just need to know the charge as its obviously not in the periodic table. Phosphate has a charge of -3 with the formula of PO4. So Sodium Phosphate is Na3(PO4), 3 sodium’s (+1*3) to cancel out the -3 charge on the phosphate. You put phosphate in brackets to indicate that it goes together. So Calcium Phosphate is Ca3(PO4)2, (3*+2) + (2*-3) = 0.

Your total equation without balancing is

Na3(PO4) + CaCl2 => Ca3(PO4)2 + NaCl

If you count each type of atom you have different numbers. So now you have to balance the equation. And you get

2Na3(PO4) + 3CaCl2 => Ca3(PO4)2 + 6NaCl

Hope this helps

The answer above is good, however, these atoms don't have charge. They are neutral. Where the above poster says "charge" you should be using the word "valence".

Other than that it's a well written answer.