In a compound P2O5, the ratio of phosphorous to oxygen atoms is 2:5. Because there are two phosphorous atoms and five oxygen atoms. Both combined are called a P2O5.
The elements of phosphorous and oxygen are added to P2O5. So P2O5 is called as phosphorous pentoxide. The element phosphorous will be added to oxygen and it will form a chemical reaction.
This includes a change in the energy of P2O5. So the new energy will be produced.
