Hydrobromic acid (HBr) is a compressed liquified gas and Sulfur dioxide (SO2) is a colorless liquified gas with a pungent odor. Let us discuss the reaction between the two.
HBr is one of the most potent acids and a reducing agent. SO2 is an acidic oxide and has an oxidizing property as well. So the reaction between a reducing agent and an oxidizing agent will give us some new ideas about how the chemical reaction proceeds.
In this article, we will discuss the products, how to balance the reaction, reversibility, type, and many more facts about the reaction between HBr and SO2 in more depth.
What is the product of HBr and SO2?
The obtained products are solid sulfur (S), a reddish-brown bromine gas (Br2), and water (H2O) from the reaction between hydrogen bromide(HBr) and sulfur dioxide(SO2).
The reaction is:-
HBr(aq) +SO2(aq) ➝ H2O(l)+ S (s)+ Br2(aq)
What type of reaction is HBr+ SO2?
The reaction between HBr and SO2 is the type of Redox reaction, Irreversible reaction, Endothermic reaction, and Precipitation reaction.
How to balance HBr + SO2?
To balance the reaction of HBr +SO2, the given steps are to be followed in the Oxidation number method:-
- First, find the oxidation numbers of each atom to find which atoms are oxidized and reduced.
- HBr(aq) +SO2(aq) ➝ H2O(l)+ S (s)+ Br2(aq) — From this reaction, the oxidation states generated by each atom are shown in the table below.
| Atoms | O.N. on the reactant side | O.N. on the product side |
|---|---|---|
| Br | -1 | 0 |
| S | +4 | 0 |
| O | -2 | -2 |
- From the O.N. count, Br is oxidized (-1 to 0) and S is reduced (+4 to 0) here.
- The increase in O.N. of Br =0 – (-1) =1 unit
- The decrease in O.N. of S =(+4)- (0)= 4 unit
- To balance this equation, S and Br need to be in a 1:4 ratio.
- Balance H2O by checking the oxygen atoms on both sides.
- Therefore, the final balanced equation is:-
S(IV)O2 (aq) + 4HBr(-1)(aq) = S(0)(s) +2Br2(0) +2H2O
HBr + SO2 titration
The titration between HBr and SO2 cannot be done directly as HBr is a strong acid and SO2 is also an acidic oxide and SO2 is in a gaseous state.
HBr + SO2 net ionic equation
The net ionic equation of HBr + SO2 is:-
S(IV)O2 (aq) + 4H+(aq) + 4Br –(aq)= S(0)(s) +2Br2(0) +2H+(aq) +2 OH–(aq)
- As in the reactant side HBr is a strong acid so in an aqueous solution it ionizes to H+ and Br– but
- As SO2 is an acidic oxide so it does not decompose into ions.
- In the product, side sulfur precipitated as a solid, and Br2 is a neutral covalent compound so these two do not decompose into ions.
- H2O (water) will decompose to H+ and OH– slightly.
- So the net ionic equation becomes:-
S(IV)O2 (aq) + 4H+(aq) + 4Br –(aq)= S(0)(s) +2Br2(0) +2H+(aq) +2 OH–(aq)
HBr + SO2 conjugate pairs
The conjugate pairs of the HBr + SO2 reaction are –
- As HBr is a strong acid so, in an aqueous solution, HBr donates the proton so that the Br– is the conjugate base of HBr.
- As SO2 is an acidic oxide so, it has no conjugate pair.
HBr and SO2 intermolecular forces
In HBr + SO2 reaction, the following intermolecular forces are present in the reactant molecules:
- HBr is a polar covalent strong acid. It possesses an intermolecular H- bonding interaction(strong) with other HBr molecules and Ionic dipole-dipole interactions (coulombic force of attraction) are present in between H+ and Br – to form the HBr.
- As SO2 is a polar covalent molecule so it possesses dipole-dipole interactions.
- Solid sulfur (S) possess van-der walls force of attraction as it is a nonpolar solid compound.
- In Br2 only the london-dispersion force of attraction is present as it is a nonpolar covalent molecule.
- In water (H2O) there is an intermolecular H-bonding is present.
HBr + SO2 reaction enthalpy
The net reaction enthalpy of HBr + SO2 reaction is +66.5 kJ/mol .
The standard enthalpies of the formation of reactants and products are as follows :
| Molecules | Enthalpy of formation(KJ/mol) |
|---|---|
| HBr | -36.2 |
| SO2 | -296.9 |
| H2O | -187.6 |
| Br2 | 0 |
| S | 0 |
Reaction Enthalpy ΔHf = Standard enthalpy of products – Standard enthalpy of reactants
Thus, ΔHf =[0+0+2(-187.6)]-[(-296.9)+4(-36.2)]
=+66.5 kJ/mol
Is HBr+ SO2 a buffer solution?
HBr+SO2 is not a buffer solution as HBr is a strong acid, and SO2 is an oxide, so it cannot produce any buffer solution. To produce a buffer solution, we need a mild acid and a salt of that acid that maintains the pH of the solution but here it is not possible.
Is HBr+ SO2 a complete reaction?
The HBr+ SO2 reaction is a complete reaction as no further reaction takes place after that, and no reverse reaction takes place as sulfur gets precipitated.
Is HBr + SO2 an exothermic or endothermic reaction?
The HBr+ SO2 reaction is endothermic in nature as from the reaction, The positive enthalpy value, +66.5 kJ/mol indicates that the reaction requires energy to perform the reaction in the forward direction in the form of heat.
Is HBr + SO2 a redox reaction?
The HBr+ SO2 reaction is a redox reaction where oxidation of Br(-1 to 0) and reduction of sulfur (+4 to 0) occurs simultaneously. Here HBr is a reducing agent, and SO2 is an oxidizing agent.
Is HBr + SO2 a precipitation reaction?
The HBr+ SO2 reaction is a precipitation reaction because yellow solid sulfur [S(0)] is precipitated as a product that does not dissolve in water or acid easily.
Is HBr + SO2 reversible or irreversible reaction?
The HBr+ SO2 reaction is an irreversible reaction, unidirectional, as all the reactants react to form the products, and sulfur gets precipitated, which cannot reverse back to SO2 in this reaction condition.
Is HBr + SO2 displacement reaction?
The HBr+ SO2 reaction is not a displacement reaction as no atoms are displaced by each other to form the products.
Conclusion
From the above discussion, the reaction between a strong acid (HBr) reacts with an acidic oxide (SO2) to form sulfur, which is very important for industrial uses. It is a redox reaction that can be performed at room temperature as well. So it is energy as well as cost-efficient.
Hello…I am Ayon Majumder. I have recently post-graduated from Visva-Bharati University with Organic chemistry as my specialization. Over the course of my studies, I have developed a strong grip on various topics in advanced organic chemistry. I constantly strive to be the best version of myself and to uplift the people that I work with. I am a fast learner and can take on any challenge with creativity and hard work.