Understanding the Reactions of $P_2O_5$

$P_2O_5$, or phosphorus pentoxide, is a powerful dehydrating agent. It readily reacts with substances containing hydrogen and oxygen, particularly acids, by removing water molecules and forming the corresponding anhydrides.

Reaction with $HNO_3$

When $P_2O_5$ reacts with nitric acid ($HNO_3$), it acts as a dehydrating agent, removing the elements of water from the acid to form its anhydride, dinitrogen pentoxide ($N_2O_5$).

The simplified reaction is:

$ 2 HNO_3 + P_2O_5 \rightarrow N_2O_5 + 2 HPO_3 $

The $N_2O_5$ is the anhydride of nitric acid.

Reaction with $HClO_4$

Similarly, $P_2O_5$ reacts with perchloric acid ($HClO_4$) by dehydrating it to form its anhydride, dichlorine heptoxide ($Cl_2O_7$).

The simplified reaction is:

$ 2 HClO_4 + P_2O_5 \rightarrow Cl_2O_7 + 2 HPO_3 $

The $Cl_2O_7$ is the anhydride of perchloric acid.

Conclusion

Therefore, the reaction of $P_2O_5$ with $HNO_3$ gives $N_2O_5$, and the reaction with $HClO_4$ gives $Cl_2O_7$.