13 Facts on HI + H2O2: What, How To Balance & FAQs

Hydrogen Iodide and hydrogen peroxide are inorganic compounds with chemical formulas, HI and H2O2, respectively. Let us explore more about the reaction between HI and H2O2.

H2O2 is a colorless corrosive liquid. HI is a colorless, corrosive oily liquid. H2O2 interacts with acids easily due to its basic nature.

In this article, we will learn about a few properties based on the reaction HI + H2O2, like the type of reaction, the product formed, buffer solution, conjugate pairs, etc.

What is the product of HI and H2O2?

Iodine gas ( I2) and Water (H2O) are formed when HI reacts with H2O2

H2O2 + HI → I2 + H2O

What type of reaction is HI + H2O2?

HI + H2O2 is classified as a redox reaction, producing iodine gas and water.

How to balance HI + H2O2?

The equation for the reaction between HI + H2O2 is balanced using the following steps.

  • The general equation is H2O2 + HI →  I2 + H2O
  • Calculate the number of moles of each element involved in both the reactant and product side of the reaction.
ElementsReactant sideProduct side
Number of moles on each side of the reaction
  • The number of I atoms can be balanced by adding 2 to HI on the reactant side.
  • To balance H atoms on the product side we add 2 to H2O on the product side.
  • Thus, the overall balanced reaction is given by – H2O2 + 2HI → I2 + 2H2O

HI + H2O2 net ionic equation

The net ionic equation between H2O2 + HI is – H2O + H+ + I = I2 + H2O

The following steps are followed to derive the net ionic equation:

  • Write the balanced molecular equation along with the physical state.
  • H2O2 + 2HI →I2 + 2H2O
  • Now, write the ionic form of each of the substances existing in aqueous form and capable of complete dissociation in water. HI  is a weak acid that does not completely dissociate into ions in an aqueous form. Hence, the complete ionic equation is – H2O + OH + H+ + I = I2 + H2O
  • We find that the complete ionic equation is identical to the net ionic equation.
  • H2O + OH + H+ + I = I2 + H2O

HI + H2O2  conjugate pairs

The conjugate pairs of H2O2 and HI are as follows:

  • Iis the conjugate base of HI.
  • The Conjugate acid of H2O2 is H+.

HI + H2Ointermolecular forces

The intermolecular forces in H2O2 and HI are as follows:

  • Dipole-dipole interactions and dispersion forces are observed in HI. This is because HI is a polar molecule due to the difference in electronegativity of the H and I atoms.
  • However, for H2O2, the major intermolecular force is the ionic bond between the hydrogen and hydroxyl ions.

HI + H2O2  reaction enthalpy

The enthalpy of the reaction for HI + H2O2 is –188.26 kcal/ mol.

Is HI + H2O2 a buffer solution?

HI + H2O2 is not a buffer solution. A buffer solution is always the mixture of a strong acid or base and it’s corresponding salt. This is not the case for HI + H2O2 reaction mixture.

Is HI + H2O2 a complete reaction?

HI + H2O2 is a not complete reaction, as H2O2, does not dissociate completely in reaction. 

Is HI + H2O2 an exothermic or endothermic reaction?

HI + H2O2 is an exothermic reaction as the reaction enthalpy is negative.

Is HI + H2O2 a precipitation reaction?

The reaction between HI + H2O2 is an example of a displacement reaction, where insoluble I2 gas is released as the product. 

Is HI + H2O2 an irreversible reaction?

HI + H2O2 is an irreversible reaction because of the formation of iodine gas which is released from the reaction medium. 

Is HI + H2O2 a displacement reaction?

The reaction between HI + H2O2 is a displacement reaction.  


Hydrogen Peroxide and Hydrogen Iodide react to yield Iodine gas as a product. This reaction is a very popular displacement reaction. Also, I2 is widely used in printing inks and dyes, catalysts, animal feed supplements, and photographic chemicals. Iodine is also used to make polarizing filters for LCD displays.