15 Facts on HCl + O2: What, How To Balance & FAQs

Deacon process is the process of reacting hydrochloric acid with atmospheric oxygen at 400 to 500oC in the presence of different catalysts. Let us discuss in detail the reaction.

Hydrochloric acid is present in liquid and gaseous forms, usually prepared by dissolving hydrogen chloride in water. Oxygen, an oxidizing agent, is a highly reactive nonmetal and has various uses, including the production of steel, textiles, life support systems, etc. 

This article studies the balancing method, titration procedure, and detailed reaction mechanism.

What is the product of HCl and O2?

Hydrochloric acid (HCl) reacts with oxygen (O2) to form chlorine and water. Hydrogen is displaced from HCl by an oxygen atom, forming water and producing chlorine.

4HCl + O2 → 2Cl2 + 2H2O

What type of reaction is HCl + O2?

It is an endothermic, redox, and single displacement reaction. Since there is no salt formation, it is not a neutralization reaction and an acid-base reaction in the absence of a base.

How to balance HCl + O2?

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

Step 1:

the unbalanced chemical reaction is written down as follows:

HCl + O2 → Cl2 + H2O

Step 2:

Write down the number of moles of each element on the reactant side and product side, as tabulated below:

CompoundsReactant SideProduct Side
Number of moles in the reactant side and product side

Step 3:

To balance the reaction, the number of moles present in each element on the reactant side should be equal to the number of moles present in each element on the product side. Here, moles of all three elements chlorine, oxygen, and hydrogen are unbalanced.

Step 4

The following three things to be done to balance the equation:

  • HCl on the reactant side is multiplied by 2
  • Chlorine on the product side is multiplied by 2
  • Water on the product side is multiplied by 2

Step 5

Finally, the Balanced chemical reaction is –

Balance Chemical Reaction

HCl + O2 Titration

We cannot perform titration for HCl + O2 to determine the concentration of analyte, since in this example hydrochloric acid is reacted with oxygen, which is a single metal atom being the analyte, and moreover is not an acid-base reaction.

HCl + O2 net ionic equation

The net ionic equation for the given reaction is

4H+ (aq) + 4Cl (aq) + O2 (g) + = 2Cl2- (aq) + 2O2+ (aq) + 2H2 (g)

HCl + O2 conjugate pairs

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

  • HCl conjugate base = Cl
  • H2O conjugate base = OH

HCl and O2 intermolecular force

The Intermolecular forces acting on HCl and O2 are-

HCl + O2 Reaction Enthalpy

HCl reacts with O2, gives 185.04 KJ/mol, reaction enthalpy, calculated as follows:

  • Tabulate down the number of moles and respective enthalpy of each compound on the reactant side and product side as shown below
CompoundsNumber of moles Enthalpy (KJ/mol)
Number of moles and enthalpies of each compound in the reaction
  • Reaction enthalpy is calculated as follows-

Change in Enthalpy = (summation of enthalpies in product side) – (summation of enthalpies in reactant side)

  • Enthalpy Change = [2*(-241.8) + 2*(0)] – [4*(-167.15) + 1*(0)] = 185.04 KJ/mol.

Is HCl + O2 a buffer solution?

This reaction is not a buffer solution due to the presence of HCl which is a strong acid. A buffer solution is a mixture of conjugate acid and weak base or conjugate base and weak acid.

Is HCl + O2 a complete reaction?

The reaction of HCl with O2 is a complete reaction since complete moles of reactant are converted and consumed, in the product, at equilibrium.

Is HCl + O2 an exothermic or endothermic reaction?

It is an endothermic reaction since the reaction enthalpy is 185.04 KJ/mol, thereby decreasing the temperature.

Is HCl + O2 a redox reaction?

This reaction may be classified as a redox reaction, because of the reduction of oxygen molecule and oxidation of chlorine molecule.

Redox Reaction

Is HCl + O2 a precipitation reaction?

It is not a precipitate reaction since there is no salt formation throughout the reaction.

Is HCl + O2 reversible or irreversible reaction?

It is an irreversible reaction and cannot be further reverted unless there is a drastic change in pressure or temperature.

Is HCl + O2 displacement reaction?

It is a single displacement (substitution) reaction when HCl reacts with O2. In this reaction, hydrogen is traded with oxygen to form water, displacing hydrochloric acid as chlorine.


The reaction of HCl with O2 forms chlorine with various uses. The chlorine produced is used as a disinfectant and bleaching agent, used in drinking water treatment, killing bacteria, cleaning swimming pools, 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

Recent Posts