15 Facts on HCl + O3: What, How To Balance & FAQs

The reaction of strong acid (HCl) with a neutral compound (ozone) forms three different compounds. Let us examine this reaction in greater depth. 

Hydrochloric acid plays an important role as an industrial chemical and laboratory reagent. Chlorine is an extremely reactive yellow-green gas with the third-highest electronegativity. Oxygen is a colorless, odorless, reactive nonmetal gas and the most abundant element in the universe.

The following article studies the detailed reaction mechanism of hydrochloric acid with ozone, the steps involved while balancing the reaction, the net ionic equation and reaction enthalpy.

What is the product of HCl and O3?

Hydrochloric acid (HCl) reacts with ozone (O3) to form chlorine, oxygen and water. Hydrogen is displaced from HCl by the ozone atom, forming water and oxygen with the formation of chlorine. The reaction is as follows-

2HCl + O3 → Cl2 + O+ H2O

What type of reaction is HCl + O3?

The reaction of HCl+O3 is an exothermic, single displacement and redox reaction.

How to balance HCl + O3?

The following steps are to be followed to balance a chemical reaction, 

  • Step 1: Write down the unbalanced chemical reaction as:
  • HCl + O3 → Cl2 + O+ H2O
  • Step 2: Tabulate the number of moles of each element on the reactant side and product side, as shown below,
CompoundsReactant SideProduct Side
The number of moles of each element on the reactant side and product side
  • Step 3: To balance the reaction, the number of moles of reactant side should be equal to the number of moles on the product side. Here, moles of all chlorine and hydrogen atoms are unbalanced.
  • Step 4: To balance the given equation, multiply 2 with HCl on the reactant side
  • Step 5: Finally, the Balanced chemical reaction is –
  • 2HCl + O3 → Cl2 + O+ H2O

HCl + O3 Titration

The HCl + O3 cannot be titrated because HCl is reacted with O3 which is not a base compound, and so is not an acid-base reaction.

HCl + O3 Net Ionic Equation

The steps followed to write the net ionic equation are as follows –

  • Determine the state or phase of each element as shown below
  • 2HCl(aq) + O3(g) = Cl2(g) + O2(g) + H2O(l)
  • Complete ionic equation is written by breaking all soluble ionic compounds into their respective ions –
  • 2H+(aq) + 2Cl(aq) + O3(g) = Cl2(g) + O2(g) + H2O(l)
  • The net ionic equation includes species involved in the reaction by removing ions in both the reactant and product sides.
  • The net ionic equation is –
  • 2H+(aq) + 2Cl(aq) + O3(g) = Cl2(g) + O2(g) + H2O(l)

HCl + O3 conjugate pairs

The conjugate acid-base pairs are observed when there is a chemical difference of one proton between acid and base compounds.

  • Conjugate base of HCl= Cl
  • Conjugate base of H2O= OH

HCl and O3 intermolecular forces

The intermolecular forces acting on HCl and O3 are-

HCl + O3 Reaction Enthalpy

HCl reacts with O3, gives 185.04 KJ/mol, reaction enthalpy. The number of moles and respective enthalpy of each compound in the reactant side and product side is tabulated below.

Enthalpy Change = [1*(-241.8) + 1*(0) + 1*(0)] – [2*(-167.15) + 1*(142.2)] = -50.18 KJ/mol.

Compounds Number of MolesEnthalpy (KJ/mol)
Number of moles and Enthalpy of each compound

Is HCl + O3 a buffer solution?

HCl + O3 reaction is not a buffer solution due to the strong presence of an acid, which is HCl.

Is HCl + O3 a complete reaction?

HCl with O3 is a complete reaction since products are completely formed when it reaches equilibrium.

Is HCl + O3 an exothermic or endothermic reaction?

It is an exothermic reaction since the enthalpy is -50.18 KJ/mol, increasing the reaction temperature.

Is HCl + O3 a redox reaction?

This reaction is classified as redox because of the reduction of oxygen molecules and oxidation of chlorine molecules.

  • Oxidation of chlorine atom
  • Reduction of oxygen atom

Detail reaction is shown below.

Redox Reaction

Is HCl + O3 a precipitation reaction?

It is not a precipitate reaction since no precipitate is formed throughout the reaction.

Is HCl + O3 reversible or irreversible reaction?

It is not a reversible reaction, unless and until there is a drastic change in temperature or pressure.

Is HCl + O3 displacement reaction?

When HCl reacts with O3, it exhibits a single displacement (substitution) reaction. In this reaction, hydrogen is traded with a single atom of ozone to form water (H2O), displacing hydrochloric acid as chlorine (Cl)and ozone as oxygen (O2).


Hydrochloric acid reacts with ozone to form chlorine, oxygen and hydrogen, which has a variety of industrial uses. Chlorine is extensively used for bleaching in paper and textile industries to produce many organic and inorganic chemicals. Oxygen gas can remove pollutants from water in water purification sewage treatment plants, while water is largely used in cooling towers, boilers etc.

Pratham Shah

Hi....I am Pratham Manish Shah, Pursuing an Integrated MTech degree in Chemical Engineering from the Institute of Chemical Technology Mumbai Marathwada Jalna. With Lamdageeks, I am Interested in learning ongoing education opportunities to maintain knowledge of emerging technologies and methods. Let's connect via LinkedIn: www.linkedin.com/in/pratham-shah-07

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