Ethane Formula: Structure, Property, Uses, Examples

Ethane Formula is \(C_2H_6\). We all know that natural gas used as fuel for warming up our homes and cooking consists of methane, but we know ethane also forms a part of this natural gas. It is the second-largest percentage in natural gas. 

Ethane is a colourless, odourless, and flammable gas. Michael Faraday was the first to synthesise ethane, an organic chemical molecule, in \(1834\). In this article, let us learn more about the ethane formula, its formation, structure, and types. 

Ethane Structure

The Ethane structure is discussed below:

Ethane Formula

Ethane is only composed of carbon and hydrogen atoms, so it is classified as a hydrocarbon. It is a two-carbon containing saturated hydrocarbons consisting of only sigma bonds. The chemical formula of Ethane is \({{\rm{C}}_2}{{\rm{H}}_6}\) and its chemical structure is shown below.

Study About Homologous Series

Ethane Molar Mass

The Ethane molar mass can be written as, \({{\rm{C}}_2}{{\rm{H}}_6} = 2\) (Atomic mass of carbon) \( + 6\) (Atomic mass of hydrogen)
\( = 2(12.01) + 6(1.007) = 30.07\;{\rm{g}}/{\rm{mol}}\)

Hence, one mole of Ethane weighs \(30.07\) grams.

Ethane Hybridisation

Hybridisation results in the formation of new hybrid orbitals by mixing up atomic orbitals. These hybrid orbitals are generally of lower energy and suitable for the pairing of electrons to form chemical bonds. In Ethane, each carbon atom is \({\rm{s}}{{\rm{p}}^3}\) hybridised.

The ground state of each carbon atom in an ethane molecule has two electrons in its \(2\;{\rm{s}}\) orbital and \(1\) electron each in \(2{\rm{Px}}\) and \(2{\rm{Py}}\) orbital. The \(2{\rm{Pz}}\) orbital is empty. In its excited state, one paired electron from the \(2\;{\rm{s}}\) orbital jumps to occupy the empty \(2{\rm{Pz}}\) orbital.

Hence, there are four orbitals, \({\rm{ 2s, }}2{\rm{Px}},2{\rm{Py}},\) and \(2{\rm{Pz}}\), in each carbon atom that overlaps and form singly paired orbitals. These orbitals readily accept electrons from other atoms and form sigma bonds.

Hence, in Ethane consisting of two carbon atoms, there are eight \({\rm{s}}{{\rm{p}}^3}\) hybridised orbitals. Out of these eight orbitals, six orbitals are involved in \({\rm{s}}{{\rm{p}}^3} – {\rm{s}}\) sigma bonding with the hydrogen atoms. The remaining two hybridised orbitals overlap with each other to form a sigma bond. This is diagrammatically represented as below-

Molecular Geometry of Ethane

Ethane can be viewed as a dimer of a methyl group. The shape of the methyl group is a tetrahedral arrangement, with an angle of \(109°28’\). When the ethane molecule is put together, the arrangement around each carbon atom is again tetrahedral with approximately \(109°28’\) bond angles.

Bond Angle of Ethane

Ethane, \({{\rm{C}}_2}{{\rm{H}}_6}\) has a geometry related to that of methane. The two carbons are bonded together, and each is bonded to three hydrogens. Each H-C-H angle is \(109°28’\), and each H-C-C angle is \({109.28^\prime }\). The carbon-hydrogen σ bonds are slightly weaker (bond dissociation enthalpy of \(421\;{\rm{kJ}}/{\rm{mol}}\)) than those of methane.

Dipole Moment of Ethane

The polarity of the molecule is obtained when there is a net dipole moment in the molecule. Ethane is nonpolar because there is no difference in electronegativity between the \(2\) carbons, and the difference in electronegativity between C and H is minimal. This is the reason why alkanes, in general, are considered nonpolar.

Lewis Structure of Ethane

Lewis structures (also known as Lewis dot structures or electron dot structures) are diagrams that represent the valence electrons of atoms within a molecule. Each dot represents an electron, and a pair of dots between chemical symbols for atoms represents a bond. In \({{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{2}}},\) there are \(14\) valence electrons distributed as follows.

Skeletal Structure of Ethane

Ethane is a colourless, odourless, and flammable gas having two carbon (C) atoms and six hydrogens (H) atoms. It’s only composed of carbon and hydrogen atoms, so it is classified as a hydrocarbon. The two carbon atoms are bonded together, and three hydrogen atoms are attached to each carbon atom. All of the bonds that we see here are sigma bonds. For this reason, Ethane is classified as an alkane. An alkane is a chemical compound that consists of hydrogen and carbon atoms and is only made of sigma bonds.

Three-dimensional Representation of Ethane

The three-dimensional structure of an organic compound is represented by the Wedge-dash method that has the following aspects:

1. A solid wedge – for a bond that protrudes out of the plane of paper towards the viewer.
2. A dashed wedge – for a bond that projects away from the viewer or into the plane of the paper.
3. A solid line – for a bond that lies in the plane of the paper.

Considering the above factors, Ethane can be represented as follows-

In Ethane, the different spatial arrangements of hydrogen atoms are readily interconvertible by rotation about C-C single bonds. This phenomenon of different spatial arrangements due to C-C single bond rotation is known as confirmation. Conformations represent conformers that are readily interconvertible and thus nonseparable. Conformers are the exact same molecule that differs only in the rotation of one or more sigma bonds.

There are seven sigma bonds in the ethane molecule, but rotation about the six carbon-hydrogen bonds does not result in any change in the shape of the molecule. This is because the hydrogen atoms are essentially spherical and rotation of the C-H bond do not lead to any specific change in the shape. Rotation about the carbon-carbon bond, however, results in many different possible molecular conformations.

To better visualise these different conformations, it is convenient to use a drawing convention called the Newman projection. In a Newman projection, we look lengthwise down a specific bond of interest. We depict the ‘front’ atom as a dot and the ‘back’ atom as a larger circle.

Conformers of Ethane are represented through Newman projection, as shown below.

When an ethane molecule rotates about its carbon – Carbon single bond, two extreme conformations can result in the staggered conformation and the eclipsed conformation. The six carbon-hydrogen bonds are shown as solid lines protruding from the two carbons at \(120°\) angles. This is the actual two-dimensional tetrahedral geometry of Ethane.

Staggered Conformation: The lowest energy conformation of Ethane, shown in the figure above, is the ‘staggered’ conformation. In this conformation, all of the C-H bonds on the front carbon atom are at a dihedral angle of \(60°\) relative to the C-H bonds on the back carbon.

This angle between a sigma bond on the front carbon compared to a sigma bond on the back carbon is called the dihedral angle. In this conformation, the distance between the bonds (and the electrons in them) is maximised. Maximising the distance between the electrons decreases the electrostatic repulsion between the electrons and results in a more stable structure.

Eclipsed Conformation: Rotating the front \({\rm{C}}{{\rm{H}}_3}\) group at an angle of \(60°\) clockwise, results in the ethane molecule possessing the highest energy ‘eclipsed’ conformation. In this conformation, the hydrogens on the front carbon are as close as possible to the hydrogens on the back carbon.

Eclipsed Conformation is the highest energy conformation because of unfavourable electrostatic repulsion between the front and back C-H bonds. The energy of the eclipsed conformation is approximately \(3\,{\rm{kcal}}/{\rm{mol}}(12\;{\rm{kJ}}/{\rm{mol}})\) higher than that of the staggered conformation. 

Torsional strain (or eclipsing strain) denotes the energy difference caused by the increased electrostatic repulsion of eclipsing bonds.

Another \(60°\) rotation returns the molecule to a second staggered conformation. This process can be continued all around the \(360°\) circle. These rotations result in three possible eclipsed conformations three staggered conformations and an infinite number of skewed structures in between.

Unhindered (Free) Rotations Do Not Exist in Ethane

The carbon-carbon bond in ethane is not completely to rotate. This is due to the \(3\,{\rm{kcal}}/{\rm{mol}}\) torsional strain that creates a barrier to rotation about the C-C single bond.

The torsional strain must be overcome for the bond to rotate from one staggered conformation to another. At extremely cold temperatures this rotational barrier is large enough to prevent rotation. So at normal temperatures, the carbon-carbon bond is constantly rotating and is more likely to be in its stable conformation, i.e staggered conformation. This is represented by the ‘energy valleys’ in the graph below.

The potential energy associated with the various conformations of Ethane varies with the dihedral angle of the bonds. Valleys in the graph represent the low energy staggered conformers, while peaks represent the higher energy eclipsed conformers.

Sawhorse Projection

In a sawhorse projection, the backbone carbons are represented by a diagonal line, and the terminal carbons are shown in groups, just as in the Fischer projection. A sawhorse projection can reveal staggered and eclipsed conformations in molecules. Below are two Sawhorse Projections of Ethane.
The structure on the right is staggered, and the structure on the left is eclipsed. These are the simplest Sawhorse Projections because they have only two carbons, and all of the groups on the front and back carbons are identical.

Sawhorse projection also helps in explaining the stability of conformations. In the staggered form of Ethane, the carbon-hydrogen bonds are as far apart as possible. Thus, there are minimum repulsive forces, minimum energy and maximum stability of the molecule.

On the other hand, in the eclipsed form, the electron clouds of the carbon-hydrogen bonds come closer to each other, resulting in an increase in electron cloud repulsion.

Hence, the Staggered form is more stable.

Sawhorse projections are useful for determining if two molecules are enantiomers or diastereomers. They make it easier to see if the structures are mirror images or superimposable.

Preparation of Ethane

Ethane is isolated on an industrial scale from natural gas and as a by-product of petroleum refining.

Laboratory Preparation of Ethane

1. Ethane can be viewed as a dimer of methyl groups. In the laboratory, Ethane may be conveniently synthesised by the electrolysis of an aqueous solution of acetate salt. This process is known as Kolbe electrolysis.

At the anode, acetate is oxidised to produce carbon dioxide and methyl radicals, and the highly reactive methyl radicals combine to produce Ethane:

\({\rm{C}}{{\rm{H}}_3}{\rm{CO}}{{\rm{O}}^ – } \to {\rm{CH}}_3^{\rm{o}} + {\rm{C}}{{\rm{O}}_2} + {{\rm{e}}^ – }\)
\({\rm{CH}}_3^{\rm{o}} + {\rm{CH}}_3^{\rm{o}} \to {{\rm{C}}_2}{{\rm{H}}_6}\)

2. Ethane is also prepared by the Wurtz reaction. When methyl bromide or methyl iodide and sodium are heated in the presence of dry ether, Ethane is formed.

\({\rm{C}}{{\rm{H}}_3}{\rm{I}} + {\rm{Na}} + {\rm{C}}{{\rm{H}}_3}{\rm{I}} \to {\rm{C}}{{\rm{H}}_3} – {\rm{C}}{{\rm{H}}_3} + {\rm{NaI}}\)

Physical Properties of Ethane

Chemical Properties of Ethane

1. The ethane moiety is called an ethyl group, and related compounds may be formed by replacing a hydrogen atom with another functional group. For example, an ethyl group linked to a hydroxyl group yields ethanol, the alcohol in beverages.

2. Vapours are heavier than air. Vapours can asphyxiate by the displacement of air from enclosed spaces. Direct contact can cause frostbite.

3. Like other hydrocarbons, Ethane undergoes complete combustion and produces carbon dioxide and water. It is an exothermic reaction\\(2{{\rm{C}}_2}{{\rm{H}}_6} + 7{{\rm{O}}_2} \to 4{\rm{C}}{{\rm{O}}_2} + 6{{\rm{H}}_2}{\rm{O}} + 3120\;{\rm{kJ}}\)

4. Combustion may also occur without excess oxygen, forming a mix of amorphous carbon and carbon monoxide.
\(2{{\rm{C}}_2}{{\rm{H}}_6} + 4{{\rm{O}}_2} \to 2{\rm{C}} + 2{\rm{CO}} + 6{{\rm{H}}_2}{\rm{O}} + {\rm{ energy }}\)

5. Ethyl radical with oxygen results in peroxide formation, which further combines with alkanes to form ethoxy and hydroxyl radicals.
\({{\rm{C}}_2}{\rm{H}}_5^{^ \bullet } + {{\rm{O}}_2} \to {{\rm{C}}_2}{{\rm{H}}_5}{\rm{O}}{{\rm{O}}^ \bullet }\)
\({{\rm{C}}_2}{{\rm{H}}_5}{\rm{O}}{{\rm{O}}^ \bullet } + {\rm{HR}} \to {{\rm{C}}_2}{{\rm{H}}_5}{\rm{OOH}} + {{\rm{R}}^ \bullet }\)
\({{\rm{C}}_2}{{\rm{H}}_5}{\rm{OOH}} \to {{\rm{C}}_2}{{\rm{H}}_5}{{\rm{O}}^ \bullet } + {\rm{O}}{{\rm{H}}^ \bullet }\)

6. Incomplete combustion of ethane forms single-carbon compounds such as carbon monoxide and formaldehyde.

7. Ethane reacts with halogens, especially chlorine and bromine, by radical halogenation. This reaction proceeds through the propagation of the ethyl radical.

\({{\rm{C}}_2}{\rm{H}}_5^{^ \bullet } + {\rm{C}}{{\rm{l}}_2} \to {{\rm{C}}_2}{{\rm{H}}_5}{\rm{Cl}} + {\rm{C}}{{\rm{l}}^ \bullet }\)

Study Acetylene Formula

Uses of Ethane

1. The industrial importance of Ethane is based upon the ease with which it may be converted to Ethylene \(({{\rm{C}}_2}{{\rm{H}}_4})\) and hydrogen by pyrolysis, or cracking, when passed through hot tubes.

2. Ethane is extensively used in the preparation of ethanol, acetaldehyde and acetic acid. These compounds find use in paints, varnishes, adhesive, plastic etc.

Summary

Ethane is a major hydrocarbon essential for the manufacture of Ethylene. It differs from methane by a \({\rm{C}}{{\rm{H}}_{\rm{2}}}\) group or an atomic mass of \(14\) amu. The rotation around the C-C sigma bond accounts for the stability of the ethane molecule. It is generally represented through Newman projection and sawhorse projection. In this article, we learned the structure, properties and conformations of the ethane molecule. We also learnt its uses and the production of Ethylene from it.

FAQs

Here are some FAQs on Ethane:

Q.1: What is \({{\rm{C}}_2}{{\rm{H}}_6}\) called?
A.1: \({{\rm{C}}_2}{{\rm{H}}_6}\) is called Ethane. It ranks second in the homologous alkane series.

Q.2: What is the main use of Ethane?
A.2: The main use of Ethane is that it is used in the production of Ethylene through pyrolysis or cracking.

Q.3. What does Ethane look like?
A.3: Ethane has a tetrahedron geometry with two methyl groups at each of its ends. It looks like a dimer of methyl radical.

Q.4. What is the chemical formula of methanol?
A.4: The chemical formula of methanol is \({\rm{C}}{{\rm{H}}_3}{\rm{OH}}\). One hydrogen atom of methane is replaced by the hydroxyl group  (-OH) group.

Q.5. How can we identify Ethane from Ethene?
A.5: Ethane is an alkane and is a saturated hydrocarbon, whereas Ethene is an alkene and is unsaturated. Ethane consists of only single bonds, whereas Ethene consists of a double bond along with single bonds. Chemically we can identify by adding bromine water to both Ethane and Ethene.

Ethane : \({\rm{C}}{{\rm{H}}_3} – {\rm{C}}{{\rm{H}}_3} + {\rm{B}}{{\rm{r}}_2} \to {\rm{no}}\,{\rm{colour}}\,{\rm{change}}\)

Ethene : \({\rm{C}}{{\rm{H}}_2} = {\rm{C}}{{\rm{H}}_2} + {\rm{B}}{{\rm{r}}_2} \to {\rm{C}}{{\rm{H}}_2}{\rm{Br}} – {\rm{C}}{{\rm{H}}_2}{\rm{Br}}:{\rm{Colour}}\,{\rm{change}}\)

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