What does the Law of Conservation of Energy say?

The law says the sum of all forms of energy is constant :)

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.