Re: I need help balancing the equation Ca3P2O8 +C+SiO2 ---> CaSiO3+COP4.

First, I presume that the equation you are talking about involves the carbon reduction of phosphate in a 
furnace to produce elemental phosphorus as a simple substance. It should read

Ca3P2O8 + C + SiO2 --> CaSiO3 + CO + P4

There is no sure-fire way to balance a chemical equation. But this is not a bad way to set about it. Find 
the most complicated looking chemical formula in the reaction (in this case Ca3P2O8) and start out 
with 1 mole of that as a tentative starting point.

Straight away, though, you can see that that is not going to work too well, because you are going to 
need 2 mole of this stuff to get 4 mole of phosphorus atoms for 1 mole of P4.

So the starting point is 2 Ca3P2O8 and 1 P4

There are now 6 mole of Ca on the reactants side, so we need 6 mole on the product side

This gives us 6 CaSiO3

6 mole of Si atoms on the product side means we need 6 mole among the reactants,

therefore 6 SiO2

Now, at last, we are in a position to tackle oxygen. Among the reactants we have 16 mole of oxygen 
atoms in the 2 Ca3P2O8 and 12 mole of oxygen atoms in the 6 SiO2 for a total of 28 mole of oxygen 
atoms. On the product side we have 18 mole of oxygen atoms in the 6 CaSiO3, which leaves 10 that 
must be in the CO.

Therefore 10 CO, and to get 10 CO we must have 10 C.

That reasoning leads us to our final balanced equation. After going through a process like this, always 
count up the number of atoms of each type on each side of the equation as a final check.