15 Facts on HCl + P2O5 What, How To Balance & FAQs

HCl is an acid and P2O5 is an oxide of phosphorous. Let us study about the reaction HCl+P2O5.

HCl is a strong corrosive, colorless acid which reacts with P2O5, one of the oxides of phosphorous. P2O5 is a white solid without any specific smell.

Here, we will discuss all the vital aspects of the reaction between HCl and P2O5 in this article.

What is the product of HCl and P2O5

The products of the reaction are phosphorous oxychloride (POCl3) and metaphosphoric acid (HPO3). The reaction is as follows.

HCl + P2O5  =  POCl3 + HPO3

What type of reaction is HCl + P2O5

This reaction does not fall under any particular type of reaction.

How to balance HCl + P2O5

The unbalanced equation for the reaction is

HCl + P2O5  =  POCl3 + HPO3

The following steps are followed to balance the equation-

  • First, number of atoms- H, Cl, P, and O on both the reactant side and product side is checked.
  • If the numbers are not same, we have to multiply the formulas of the compounds by the smallest figure as required in cases where it is not same.
  • In the unbalanced equation, the number of P and H is the same on both sides.
  • The number of Cl atoms on left hand side and right hand side is 1 and 3 respectively. So, we will multiply HCl by 3.
  • 3HCl + P2O5  =  POCl3 + HPO3
  • Now, the number of H atoms on left hand side and right hand side is 3 and 1 respectively. So, we will multiply HPO3 by 3.
  • 3HCl + P2O5  =  POCl3 + 3HPO3
  • Next, the number of O atoms on left hand side and right hand side is 5 and 10 respectively. So, we will multiply P2O5 by 2.
  • The balanced equation is
  • 3HCl + 2P2O5 =  POCl3 + 3HPO3

HCl + P2O5 titration

The titration between HCl and P2O5 is not possible because it does not fulfill any category of titration methods due to their reaction between a strong acid and an oxide.

HCl + P2O5 net ionic equation

An ionic equation for HCl + P2O5  reaction is not possible as, except for HCl, we cannot write the other three compounds as dissociated ions. P2O5, POCl3, and HPO3 are all covalent compounds.

HCl + P2O5 conjugate pairs

HCl + P2O5  =  POCl3 + HPO3

  • The conjugate base of HCl is Cl.
  • Conjugate pair is not possible for P2O5 as it is not an acid or base.

HCl + P2O5 intermolecular forces

  • Dipole-dipole and London dispersion forces; are the two intermolecular forces in HCl. Among these, the first one is predominant in HCl.
  • In P2O5, weak van der Waals forces are present.

HCl + P2O5 reaction enthalpy

The value of reaction enthalpy for HCl + P2O5  reaction is -2341.5 kJ/mol.

Is HCl + P2O5 a buffer solution

A buffer solution will not be formed by mixing HCl and P2O5. HCl being a strong acid cannot form a buffer solution.

Is HCl + P2O5 a complete reaction

HCl + P2O5  is a complete reaction as formation of the products POCl3 and HPO3, does not further react back to produce the reactants.

Is HCl + P2O5 an exothermic or endothermic reaction

HCl + P2O5  reaction is exothermic as heat is liberated.

Is HCl + P2O5 a redox reaction

The reaction HCl+P2O5 is not a redox reaction because in the molecules HCl, P2O5, HPO3, and POCl3 oxidation state does not change.

Is HCl + P2O5 a precipitation reaction

HCl + P2O5  reaction is not an example of a precipitation reaction as the product POCl3 is liquid and HPO3 is a water soluble solid.

Is HCl + P2O5 reversible or irreversible reaction

HCl + P2O5  reaction is an example of irreversible reaction as it proceeds in one direction only.

Is HCl + P2Odisplacement reaction

HCl + P2O5  is not a displacement reaction as one part of the reactant is not replaced by another reactant.


In conclusion, when hydrochloric acid reacts with phosphorus pentoxide, the products are HPO3 and POCl3. HPO3, the soft, colorless solid, dissolves slowly in cold water and deliquesces in nature.

Tuluma Das

Hello, I am Tuluma Das, Completed my Ph.D. in Organic Chemistry from the Indian Association for the Cultivation of Science. I have a total of 9 years of research experience including a Ph.D. and Postdoc and 3 years of teaching experience. I have published 7 papers so far in international journals. Let’s connect through Linkedin : https://www.linkedin.com/in/tuluma-das-90887a99/

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