Could somebody please explain how to write a balanced chemical equation for the following:?

Several are possible based on the conditions.  If the acid is concentrated, you would get complete replacement of hydrogen with calcium.   So the UNBALANCED equation is
   Ca +  H3PO4  -> Ca3(PO4)2 + H2
We know that the calcium phosphate formula is correct since Ca ion has a (+2) charge and phosphate has a (-3) charge.
To balance this, we want to ensure that
a. As many atoms of each element are on one side as another
b. There are no fractional coefficients.
First, we need to balance the Ca:
  We can double the phosphoric acid so there are 2 PO4 groups on either side.
   If we do that, we need to have 3 Ca on the left side.  No sweat.  
   If we double the PO4, we also double the available H.   This gives us 6 H.  This is good, since hydrogen gas is a dimer (H-H), and we have 3 of these in the balanced form.  
   Then we have:
 3 Ca + 2 H3PO4 -> Ca3(PO4)2 + 3 H2.

3Ca +  2H3PO4 = Ca3(PO4)2 + 3H2

Rite this is pretty hard to answer through yahhoo answers as i kinda need to be able to rite in diff font sizes. oh well i try.
First rite out a word equation for the reaction:
calcium + phosphoric acid = calcium phosphate + hydrogen.

(remember this; metals + acids = salt+ hydrogen.)

then you need to find the symbols for each element.

Calcium = Ca
Phosphoric acid = H3PO4
Hydrogen = H2
Calium Phosphate = CaH3PO4 (i fink!) im not 100% sure.

hopefully them symbols are rite. Now, get ur word equation and rewrite it only this time, you substitue the chemical names for there symbols.

Ca + H3PO4 = CaH3PO4 + H2

Now however you must check its balanced. which is hard to explain. You need to count the number of atoms on each side.
Ca =1
H3=3
P=1
O=4
H2= 2

Now create an imaginary line dividing the sides that are separated by the equals sign.
so we have  left side (ca + H3PO4)
and the rite side (CaH3PO4 + H2 )

No we count up the number of atoms on each side.

Left = 9
Rite = 11

We need to make both of those numbers the same to make it balanced.
So we have to times one of these by something. Ive worked out that we need to times the left Ca by 3.
So the balanced eqaution is=

3 Ca + H3PO4 = CaH3PO4 +H2

plz not if the number has a space between the letter and the number, rite normal size.
if it is ritten next to the letter, rite it small, bellow the line.

I hope thats helped you. its really hard to explain it thru yahhoo answers, but i hope u got the jist of things. ask your chemistry teacher for help if u still cant rite balanced eqautions. I sure she/he wud be happy to help.
Plus its so much easier to learn when theres a witebord to learn from!