Question

Complete and balance the following reaction:

$\mathrm{HCl}\rightleftharpoons$

Answer 1

Step 1: Thermal dissociation

• When Hydrogen chloride ($\mathbf{HCl}$) is heated above 500^°C, It dissociates into Hydrogen (${\mathbf{H}}_{\mathbf{2}}$) and Chlorine (${\mathbf{Cl}}_{\mathbf{2}}$)
• Thermal decomposition reaction of Hydrogen chloride is $\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{\mathrm{HCl}\left(\mathrm{g}\right)}\stackrel{>500°\mathrm{C}}{\rightleftharpoons }\underset{\left(\mathrm{Hydrogen}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Chlorine}\right)}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}$

Step 2: Acidic properties

• When dissolve in water Hydrogen chloride changes to form Hydrochloric acid.
• Hydrochloric acid dissociates further into Hydrogen and Chlorine ion.
• Decomposition reaction of Hydrochloric acid is as follows: $$\begin{gathered} \mathrm{HCl}\left(\mathrm{aq}\right)\stackrel{{\mathrm{H}}_2\mathrm{O}}{\rightleftharpoons }{\mathrm{H}}^{+}+{\mathrm{Cl}}^{-} \\ \mathrm{Hydrogen}\mathrm{Hydrogen}\mathrm{Chlorine} \\ \mathrm{chloride}\mathrm{ion}\mathrm{ion} \end{gathered}$$.

Step 3: Balancing the equation:

• The obtained reaction is unbalanced in nature, so first, we calculate the number of molecules on both sides of the reaction.
• On the reactant side: 1 Hydrogen and 1 Chlorine are present in Hydrogen chloride.
• On the product side: 2 molecules of Hydrogen and 2 molecules of Chlorine are present.

Step 4: Balancing the product molecules: by multiplying Hydrogen chloride with 2.

• The chemical equation is as follows:$\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{2\mathrm{HCl}\left(\mathrm{g}\right)}\stackrel{>500°\mathrm{C}}{\rightleftharpoons }\underset{\left(\mathrm{Hydrogen}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Chlorine}\right)}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}$
• The total number of molecules on both sides of the reaction is equal.

Hence, the balanced chemical equation is as follows: $\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{2\mathrm{HCl}\left(\mathrm{g}\right)}\stackrel{>500°\mathrm{C}}{\rightleftharpoons }\underset{\left(\mathrm{Hydrogen}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Chlorine}\right)}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}$