Question

For which of the following reactions, is Gay-Lussac’s law not applicable?

• A. formation of HI from its constituents
• B. formation of NH₃ from its constituents
• C. Formation of CO₂ from its constituents
• D. Formation of SO₃ from SO₂ and O₂

Answer 1

The correct option is C

Formation of CO₂ from its constituents

Explanation for the correct answer:

Gay-Lussac’s law of combining volumes of gases:

Gases react chemically in volumes that bear a simple whole-number ratio to each other and to the volumes of the products given that they are also in the gaseous state and the reaction conditions of temperature and pressure are also same for them.

$$\begin{gathered} \mathrm{C}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right) \\ \left(\mathrm{Carbon}\right)\left(\mathrm{Oxygen}\right)(\mathrm{Carbon}\mathrm{dioxide}) \end{gathered}$$

In this reaction, Carbon (C) exists in the solid-state but Gay-Lussac's law is applicable only to the gaseous reactants and products. Therefore, Gay-Lussac’s law is not applicable to the formation of CO₂ from its constituents.

Explanation for the incorrect answer:

All the following options follow gas laws because they are in the gaseous state and bear a simple whole-number ratio to one another.

(a) Formation of HI from its constituents

$$\begin{gathered} {\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{I}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{HI}\left(\mathrm{g}\right) \\ \left(\mathrm{Hydrogen}\right)\left(\mathrm{Iodine}\right)(\mathrm{Hydrogen}\mathrm{Iodide}) \end{gathered}$$

Ratio= 1:1:2 by volume

(b) Formation of NH₃ from its constituents

$$\begin{gathered} {\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\stackrel{450°\mathrm{C},250\mathrm{atm},\mathrm{Fe}/\mathrm{Mo}}{\rightleftharpoons }2{\mathrm{NH}}_3\left(\mathrm{g}\right) \\ \left(\mathrm{Nitrogen}\right)\left(\mathrm{Hydrogen}\right)\left(\mathrm{Ammonia}\right) \end{gathered}$$

Ratio= 1:3:2 by volume

(d) Formation of SO₃ from SO₂ and O₂

$$\begin{gathered} 2{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{SO}}_3\left(\mathrm{g}\right) \\ (\mathrm{Sulphur}\mathrm{dioxide})\left(\mathrm{Oxygen}\right)(\mathrm{Sulphur}\mathrm{trioxide}) \end{gathered}$$

Ratio= 2:1:2 by volume

Hence, option (c) is correct.