13 Facts on H2SO4 + P2O5: What, How To Balance & FAQs

Sulphuric acid (H2SO4) is a colourless, viscous liquid and phosphorus pentoxide (P2O5) is a strong dehydrating agent. Let us take a glance at how these two react to each other.

Phosphorus oxide is not as strong an acid as much as sulphuric acid; it is an acidic oxide that works well as a desiccating agent.

We will dive deep into the facts about reactions between H2SO4 and P2O5, like reaction enthalpy, type of reaction, conjugate pairs, intermolecular forces etc.,

What is the product of H2SO4 and P2O5

Sulphur trioxide and meta-phosphoric acids are formed when sulphuric acid (H2SO4) is heated in the presence of phosphorus pentoxide, which has to be taken in excess.

H2SO4 + P2O5 = SO3 + HPO3

What type of reaction is H2SO4 and P2O5

The reaction between H2SO4 and P2O5 is a double-displacement reaction.

How to balance H2SO4 and P2O5

The reaction between H2SO4 and P2O5 can be balanced using the steps mentioned below,

  • Writing the general chemical equation:
  • H2SO4 + P2O5 = SO3 + HPO3
  • We need to check whether the number of atoms on the reactant and product side is equal. But as we can see, the number of hydrogens, oxygens and phosphorus need to be balanced throughout the equation.
  • Therefore we will multiply a coefficient of 2 with metaphosphoric acid to get the new equation.
  • H2SO4 + P2O5 = SO3 + 2HPO3
  • Counting down the number of atoms present on both sides of the chemical equation;
AtomsNumber on reactant sideNumber on product side
Number of Atoms
  • As the number of atoms gets equated, the new balanced chemical equation is
  • H2SO4 + P2O5 = SO3 + 2HPO3

H2SO4 and P2O5 titration

The titration between H2SO4 and P2O5 is not feasible as both are acids and thus the end-point during the titration cannot be determined.

H2SO4 and P2O5 net ionic equation

The net ionic equation for H2SO4 + P2O5 reaction is,

SO42- (aq.) + P2O5 (aq.) = SO3 (g) + PO3 (aq.)

  • The general balanced equation for H2SO4 + P2O5 is
  • H2SO4 + P2O5 = SO3 + 2HPO3
  • Indicating the chemical states of each molecule
  • H2SO4 (aq.) + P2O5 (aq.) = SO3 (g) + 2HPO3 (aq.)
  • Split the soluble compounds into their respective ions.
  • 2H+ (aq.) + SO42- (aq.) + P2O5 (aq.) = SO3 (g) + 2H+ (aq.) + PO3 (aq.)
  • Cancel out the ions which are present on both sides to get the net ionic equation.
  • SO42- (aq.) + P2O5 (aq.) = SO3 (g) + PO3 (aq.)

H2SO4 and P2O5 conjugate pairs

In the following reaction,

H2SO4 + P2O5 = SO3 + 2HPO3

  • The Conjugate pair for reactant H2SO4 is HSO4
  • The Conjugate pair for HPO3 is PO3

The other two, i.e., P2O5 and SO3, do not have any conjugate pairs because they lack hydrogen in their chemical formula.

H2SO4 and P2O5 intermolecular forces

The H2SO4 + P2O5 reaction has the following intermolecular forces between the molecules,

Molecules Intermolecular forces
H2SO41. Van der Waals dispersion forces
2. dipole-dipole interactions
P2O5Weak van der waal forces
SO3London-dispersion forces
Intermolecular forces between H2SO4 and P2O5

Is H2SO4 and P2O5 a buffer solution

H2SO4 + P2O5 reaction cannot yield a buffer solution as both chemicals have an acidic nature having variations in the strength of acidity. That is why if more acid is added to the solution, the pH value will decrease further, which should not happen in the case of a buffer solution.

Is H2SO4 and P2O5 a complete reaction

H2SO4 + P2O5 reaction is a complete reaction as sulphuric acid, and phosphorus pentoxide is completely used to form meta-phosphoric acid with sulphur trioxide.

Is H2SO4 and P2O5 an exothermic or endothermic reaction

H2SO4 + P2O5 reaction is an endothermic chemical reaction because heat is needed at the beginning of the reaction to initiate the process.

Is H2SO4 and P2O5 a redox reaction

H2SO4 + P2O5 reaction is not a redox reaction because the oxidation states of atoms have remained unchanged throughout the process.

Is H2SO4 and P2O5 a precipitation reaction

H2SO4 + P2O5 reaction is not a precipitation reaction as H2SO4 and P2O5 reaction do not yield any precipitates.

Is H2SO4 and P2O5 reversible or irreversible reaction

H2SO4 + P2O5 reaction is irreversible reaction because the SO3 released cannot be added back to the reaction until an immense high pressure is applied, which is not possible normally.

Is H2SO4 and P2O5 displacement reaction

H2SO4 + P2O5 reaction is a double-displacement reaction. Here, P2O5 acting as a dehydrator removes water from sulphuric acid to form meta-phosphoric acid.


The article concludes that both sulphuric acid and phosphorus pentoxide are reacting with each other being acids and P2O5 is a stronger dehydrating agent than sulphuric acid. These chemicals have several industrial and laboratory importance.

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