##”P”_4″O”_text(10(s]) + 6″H”_2″O”_text((l]) -> 4″H”_3″PO”_text(4(aq])##

The interesting thing about diphosphorus pentoxide, ##”P”_2″O”_5##, is that it usually exists as a dimer.

This implies that ##”P”_2″O”_5## is actually the compound’s and that you should use ##”P”_4″O”_10## as its molecular formula.

Now, diphosphorus pentoxide reacts violently with water to form phosphoric acid, ##”H”_3″PO”_4##. The reaction is highly exothermic and leads to the formation of toxic fumes.

The unbalanced chemical equation for this reaction looks like this

##”P”_4″O”_text(10(s]) + “H”_2″O”_text((l]) -> “H”_3″PO”_text(4(aq])##

To balance this equation, start by multiplying the phosphoric acid by ##4## to get equal numbers of atoms of phosphorus on both sides of the equation

##”P”_4″O”_text(10(s]) + “H”_2″O”_text((l]) -> 4″H”_3″PO”_text(4(aq])##

Notice that you have ##2## atoms of hydrogen on the reactants’ side and ##12## on the products’ side. Multiply the water molecule by ##6## to balance the hydrogen atoms out.

Incidentally, this will also balance out the atoms of oxygen, since you’d now have ##16## on the reactants’ side and ##16## on the products’ side.

The balanced chemical equation for this reaction will thus be

##”P”_4″O”_text(10(s]) + 6″H”_2″O”_text((l]) -> 4″H”_3″PO”_text(4(aq])##

It’s worth mentioning that diphosphorus pentoxide is a very powerful dehydrating agent.

SIDE NOTE You’ll sometimes see this reaction written using the empirical formula of diphosphorus pentoxide, ##”P”_2″O”_5##. In that case, the balanced chemical equation will be

##”P”_2″O”_text(5(s]) + 3″H”_2″O”_text((l]) -> 2″H”_3″PO”_text(4(aq])##