# Reactions of P2O5 and P4O10 with sulfuric acid [closed]

I have seen two reactions of $$\ce{H2SO4}$$, in one it reacts with $$\ce{P2O5}$$ and in the other $$\ce{P4O10}$$.

The Reactions are as follows:

$$\ce{H2SO4 + P2O5 -> SO3 + 2HPO3}$$

$$\ce{6H2SO4 + P4O10 -> 6SO3 + 4H3PO4 }$$

Since it is a dehydration reaction the oxidation states of sulphur and phosphorous would be the same in reactant and product, this is true for both the reactions.

Are the both Products correct $$\ce{HPO3}$$ and $$\ce{H3PO4}$$ correct? If yes what I am missing?

• P2O5 and P4O10 is the same thing. Jul 3 at 12:37
• I agree with Ivan Neretin. Basically, $\ce{P4O_{10}}$ is the dimeric form of $\ce{P2O_{5}}$. Jul 3 at 12:46
• To clarify, read here. Jul 3 at 12:51
• Yes @IvanNeretin ... I agree with it but why two different products . Then may be one of them is incorrect then which one ? Jul 3 at 12:52
• @MathewMahindaratne I object. P4O10 is the only form of P2O5 (not counting the polymeric forms, that is). There is no monomer of which it is a dimer. Jul 3 at 16:16

Phosphorus pentoxide is the common name of a chemical with molecular formula $$\ce{P4O10}$$. The common name is derived from its empirical formula, $$\ce{P2O5}$$. This white crystalline solid is the anhydride of phosphoric acid:
It is a potent dehydrating agent and used as a powerful desiccant (as indicated by the exothermic nature of its hydrolysis) in limited capacity: $$\ce{P4O10 + 6H2O -> 4H3PO4} \qquad \Delta H = \pu{-177 kJ}$$
However, the desiccating power of $$\ce{P4O10}$$ is strong enough to convert many mineral acids to their anhydrides. For examples, $$\ce{H2SO4}$$ is converted to $$\ce{SO3}$$: $$\ce{P4O10 + 6H2SO4 -> 6SO3 + 4H3PO4}$$
Therefore, it can be concluded that the second reaction is the correct one (although it may or may not be balanced). The first one is incorrect, solely based on the fact that $$\ce{P2O5}$$ does not exist.