15 Facts on HBr + Mg2Si: What, How To Balance & FAQs

HBr is strong inorganic acid that can easily react with electron-deficient Mg₂Si without a catalyst. Let us predict the mechanism behind the reaction.

Mg₂Si or magnesium silicide is a lewis base because the silicon center has a vacant d orbital that is energetically accessible and can accept an electron.  It is also used as an electrophilic center because the charge density over Mg is being dragged away toward the electronegative Si site. HBr is strong acid it can easily release protons.

The reaction between HBr and Mg₂Si does not require any catalyst or temperature and pressure because one is more reactive. Now we can discuss more the mechanism of the reaction like enthalpy, redox reaction, intermolecular force, conjugate pairs, etc with an explanation in the following part of the article.

1. What is the product of HBr and Mg₂Si?

Magnesium bromide and silane are formed as major products when HBr and Mg₂Si are subject to react together.

HBr + Mg₂Si = MgBr₂ + SiH₄

2. What type of reaction is HBr + Mg₂Si?

HBr + Mg₂Si reaction is an example of a double displacement reaction, and a redox and precipitation reaction. It is also a nucleophile and electrophile reaction because the former is a nucleophile and the latter is an electrophile.

3. How to balance HBr + Mg₂Si?

HBr + Mg₂Si = MgBr₂ + SiH₄, we have to balance the equation in the following way-

• First, we label all the reactants and products by A, B, C, and D as there are four different molecules obtained for this reaction and the reaction looks like this,
• A HBr + B Mg₂Si = C MgBr₂ + D SiH₄
• Equating the coefficients for the same type of elements by rearranging them.
• After the rearrangement of coefficients of the same elements by their stoichiometric proportion, we get,
• H = A = D, Br = A = 2C, Mg = 2B = C, Si = B = D
• Using the Gaussian elimination and equating all the equations we get, A = 4, B = 1, C = 3, and D = 1
• The overall balanced equation will be,
• 4HBr + Mg₂Si = 2MgBr₂ + SiH₄

4. HBr + Mg₂Si titration

To estimate the quantity of magnesium or strength of acid we can perform a titration between Mg₂Si and HBr_.

Apparatus used

We need a burette, conical flask, burette holder, volumetric flask, and beakers for this titration.

Titre and titrant

HBr versus Mg₂Si, HBr acts as a titrant taken in the burette and the molecule to be analyzed is Mg₂Si taken in a conical flask.

Indicator

The whole titration is done in an acidic medium or acidic pH so the best suitable indicator will be phenolphthalein which gives perfect results for this titration at given pH.

Procedure

The burette is filled with standardized HBr. Mg₂Si is taken in a conical flask in solution along with respective indicators. HBr is added dropwise to the conical flask and the flask is shaken constantly. After a certain time, when the endpoint arrives, the indicator changes its color and the reaction is done.

5. HBr+ Mg₂Si net ionic equation

The net ionic equation between HBr + Mg₂Si is as follows,

H⁺(aq.) + Br^–(aq.) + 2Mg²⁺(aq.) + Si^4-(aq.) = Mg²⁺(aq.) + Br^–(aq.) + SiH₄(g)

• HBr will be ionized as proton and bromide as it is strong acid and electrolyte.
• After that Mg₂Si also dissociates into Mg²⁺ ion and Si^4- ion as it is also a strong electrolyte
• In the product part, MgBr₂ is ionized into Mg²⁺ and Br^–as it is a strong electrolyte and salt.
• SiH₄ exists in the gaseous state so it can be dissociated.

6. HBr+ Mg₂Si conjugate pairs

In the reaction, HBr+ Mg₂Si conjugate pairs will be the corresponding de-protonated and protonated form of that particular species which are listed below-

• Conjugate pair of HBr = Br^–
• Conjugate pair of SiH₄ = SiH₅⁺ (super acid)

7. HBr and Mg₂Si intermolecular forces

HBr+ Mg₂Si reaction has the following intermolecular forces,

• The intermolecular force present in HBr is the strong electrostatic force between protons and bromide ions.
• In Mg₂Si there are electronic interactions and coulumbic force present.
• In MgBr₂ ionic interaction is present and for SiH₄ van der waal’s force along with London dispersion force is present.

Molecule	Acting force
HBr	Electrostatic, van der waal’s Dipole interaction
Mg2Si	Strong electrostatic force and ionic interaction, Coulumbic force
MgBr2	Electrostatic force, ionic interaction,
SiH4	Covalent force, London dispersion force

8. HBr + Mg₂Si reaction enthalpy

HBr + Mg₂Si reaction enthalpy is -1176.78 KJ/mol which can be obtained by the formula: enthalpy of products – enthalpy of reactants.

Molecule	Enthalpy (KJ/mol)
Mg2Si	-16.69
HBr	-36.45
MgBr2	-524.3
SiH4	34.31

9. Is HBr + Mg₂Si a buffer solution?

In the reaction between HBr + Mg₂Si_, there is no such buffer formed but the mixture of MgBr₂ and SiH₄ can control the pH.

10. Is HBr + Mg₂Si a complete reaction?

The reaction between HBr + Mg₂Si is complete because it gives one major product: an electrolytic salt and other silane gas as a by-product.

11. Is HBr + Mg₂Si an exothermic or endothermic reaction?

The reaction of HBr + Mg₂Si is exothermic in terms of thermodynamics first law. This reaction released more energy and temperature to the surroundings, where δH is always negative.

12. Is HBr + Mg₂Si a redox reaction?

HBr + Mg₂Si reaction is a redox reaction because in this reaction Si gets reduced and Br gets oxidized. Where HBr acts as a reducing agent and Mg₂Si acts as an oxidizing agent.

13. Is HBr + Mg₂Si a precipitation reaction

The reaction between HBr + Mg₂Si is a precipitation reaction because Br₂ gets precipitated in the solution at certain pH.

14. Is HBr + Mg₂Si reversible or irreversible reaction?

The reaction between HBr+ Mg₂Si is irreversible because it produced silane gas. Due to the production of the gaseous molecule the entropy of the reaction increases. Therefore, equilibrium shifts towards the right-hand side only or forward directions.

4HBr + Mg₂Si —-> 2MgBr₂ + SiH₄(g)

15. Is HBr + Mg₂Si displacement reaction?

The reaction between HBr+ Mg₂Si is an example of a double displacement reaction. Because in the above reaction Br- was displaced by Mg⁺ from HBr and Si gets displaced by H⁺ from Mg₂Si.

Conclusion

The reaction between HBr and Mg₂Si is important because it can produce Silane gas. So, we have to take more cautious when the reaction is going on. It is an industrially important reaction for the production of MgBr₂ salt.