So I have to figure balance this equation.

 

_P +_O₂ ---->__P₂O₅

 

Here is my work so far;

 

2P +_O₂ ---->__P₂O₅

P=1 2 P=2

O=2 O=5

But now I am stuck trying to figure out how to get 5 oxygen on the reaction side. I was thinking 2.5, but is it possible to have decimals in the coefficient?

Thanks in advance.

Try again with 2P2O5 on the right hand side. ;-)

To elaborate a little on what DrP is saying, if you come to a situation where you have a decimal, it is acceptable to just multiply everything out by some factor to make them all whole numbers. The exception is in combustion reactions, which are routinely written with decimals.