Chemical Formula for Ethane
Chemical Formula for Ethane: Structure, Properties, and Examples
Ethane is one of the simplest hydrocarbons in organic chemistry, belonging to the alkane family. Understanding its chemical formula, structure, and properties is essential for students and enthusiasts of chemistry. This article explores the chemical formula for ethane, its molecular structure, physical and chemical properties, and some practical examples of its use.
What is Ethane?
Ethane is a colorless, odorless gas at room temperature and standard atmospheric pressure. It is primarily used as a fuel and as a raw material in the chemical industry, especially for the production of ethylene and other organic compounds.
Ethane is naturally found in natural gas and is released during the processing of crude oil. It is the second simplest alkane after methane and has gained importance in both research and industrial chemistry.
Chemical Formula of Ethane
The chemical formula of ethane is C2H6. This formula tells us that an ethane molecule consists of two carbon atoms and six hydrogen atoms.
In molecular form, ethane can be represented as:
\[ \mathrm{C_2H_6} \]
This is the molecular formula indicating the total number of each atom in a molecule of ethane.
Structural Formula of Ethane
The structural formula shows how the atoms are bonded together:
\[ \mathrm{H_3C - CH_3} \]
Each carbon atom forms four covalent bonds. In ethane, the two carbon atoms are bonded to each other with a single covalent bond, and each carbon is bonded to three hydrogen atoms. This single bond between carbons classifies ethane as an alkane (a saturated hydrocarbon).
The tetrahedral geometry around each carbon atom leads to a bond angle of approximately 109.5°, which minimizes electron pair repulsion according to the Valence Shell Electron Pair Repulsion (VSEPR) theory. This spatial arrangement influences many of ethane’s physical properties.
Lewis Structure of Ethane
The Lewis structure helps visualize the bonding between atoms and the lone pairs of electrons, although in alkanes like ethane, there are no lone pairs on carbon or hydrogen atoms.
In ethane, the Lewis structure can be represented as:
H H
\ /
H - C - C - H
/ \
H H
Each line represents a covalent bond (a pair of shared electrons). Every carbon has four bonds, satisfying the octet rule, and each hydrogen has one bond, fulfilling the duet rule.
Molecular Geometry and Bonding
Ethane’s bonding is explained by the concept of sp3 hybridization. Each carbon atom undergoes hybridization, mixing one s orbital and three p orbitals to form four equivalent sp3 hybrid orbitals. These orbitals form sigma (σ) bonds with hydrogen atoms and the other carbon atom.
This bonding makes ethane very stable under normal conditions. The C-C bond length in ethane is approximately 154 pm (picometers), while the C-H bond length is about 109 pm. These bond lengths and strengths contribute to ethane's relatively low reactivity compared to unsaturated hydrocarbons such as alkenes or alkynes.
Physical Properties of Ethane
- State at room temperature: Gas
- Color: Colorless
- Odor: Odorless
- Boiling point: −88.5 °C
- Melting point: −182.8 °C
- Density: 1.356 kg/m3 (at 15 °C and 101.325 kPa)
- Solubility: Slightly soluble in water, but soluble in organic solvents such as ethanol and ether
The low boiling and melting points are due to the weak intermolecular forces present in ethane—namely London dispersion forces, which arise from temporary dipoles. These weak forces explain why ethane exists as a gas at room temperature.
Chemical Properties of Ethane
Ethane is relatively inert compared to other hydrocarbons due to the strength of its C-C and C-H single bonds. However, it does undergo combustion and substitution reactions.
Combustion Reaction
When ethane burns in the presence of oxygen, it produces carbon dioxide and water. This is an exothermic reaction releasing energy:
\[ \mathrm{2 C_2H_6 + 7 O_2 \rightarrow 4 CO_2 + 6 H_2O} \]
The combustion of ethane releases a significant amount of heat, making it a useful fuel. The complete combustion produces the maximum energy output, but incomplete combustion can lead to the formation of carbon monoxide (CO) and soot.
Halogenation Reaction
Ethane can undergo substitution with halogens like chlorine or bromine under UV light (photochemical reaction), replacing one or more hydrogen atoms with halogen atoms. For example, chlorination produces chloroethane:
\[ \mathrm{C_2H_6 + Cl_2 \xrightarrow{UV} C_2H_5Cl + HCl} \]
This reaction proceeds via a free radical mechanism involving initiation, propagation, and termination steps. It is a classic example of radical halogenation in organic chemistry.
Other Reactions
Under high temperatures and catalysts, ethane can undergo cracking, breaking into smaller hydrocarbons, mainly ethylene (C2H4), which is an important industrial feedstock:
\[ \mathrm{C_2H_6 \xrightarrow{Heat, Catalyst} C_2H_4 + H_2} \]
This process is called steam cracking and is widely used in petrochemical industries.
Industrial and Practical Uses of Ethane
Ethane is valuable in many industrial applications:
- Production of Ethylene: Ethane is a major feedstock for ethylene production, which is further used to manufacture polyethylene (plastic), ethylene oxide, and other chemicals.
- Fuel: Ethane can be used as a fuel in residential and industrial settings, often as a component of liquefied petroleum gas (LPG).
- Refrigerant: Because of its low boiling point, ethane can be used in refrigeration systems in specialized applications.
- Laboratory Reagent: Ethane serves as a model compound in organic synthesis and mechanistic studies.
Environmental Impact of Ethane
Ethane is naturally emitted from various sources, including natural gas extraction and biomass burning. While ethane itself is not toxic, it contributes to the formation of ground-level ozone and photochemical smog, which have negative health and environmental effects.
Its release into the atmosphere is monitored as part of greenhouse gas studies, although ethane is not a greenhouse gas itself. Instead, it influences the atmospheric chemistry that affects climate change indirectly.
Handling and Safety
Ethane is highly flammable and can form explosive mixtures with air. Therefore, it must be stored and handled with proper precautions to avoid leaks, ignition sources, and accumulation in confined spaces.
Common safety measures include:
- Proper ventilation in areas where ethane is stored or used.
- Use of explosion-proof equipment.
- Regular maintenance of pipelines and containers to prevent leaks.
Example Problem: Calculating Molar Mass of Ethane
Let's calculate the molar mass of ethane (C2H6):
- Atomic mass of Carbon (C) = 12.01 g/mol
- Atomic mass of Hydrogen (H) = 1.008 g/mol
\[ \text{Molar mass of ethane} = (2 \times 12.01) + (6 \times 1.008) = 24.02 + 6.048 = 30.068 \text{ g/mol} \]
Therefore, one mole of ethane weighs approximately 30.07 grams.
Example Problem: Writing the Structural Formula in Condensed Form
Ethane's structural formula can be written in a condensed form as:
\[ \mathrm{CH_3CH_3} \]
This indicates two methyl groups bonded together.
Example Problem: Estimating Energy Released During Combustion
The standard enthalpy change for combustion of ethane is approximately −1560 kJ/mol. This means burning one mole of ethane releases 1560 kilojoules of energy:
\[ \mathrm{C_2H_6 + \frac{7}{2} O_2 \rightarrow 2 CO_2 + 3 H_2O} \quad \Delta H = -1560 \text{ kJ/mol} \]
This high energy release explains why ethane is an efficient fuel source.
Comparison of Ethane with Other Alkanes
Ethane is part of the homologous series of alkanes, where each successive member differs by a -CH2- group. Here is a brief comparison:
| Alkane | Chemical Formula | Number of Carbons | Boiling Point (°C) |
|---|---|---|---|
| Methane | CH4 | 1 | -161.5 |
| Ethane | C2H6 | 2 | -88.5 |
| Propane | C3H8 | 3 | -42.1 |
| Butane | C4H10 | 4 | -0.5 |
As the carbon chain length increases, boiling points rise due to stronger intermolecular forces. Ethane is therefore a gas at room temperature, unlike butane, which is a liquid under the same conditions.
Summary
Ethane, with the chemical formula C2H6, is a simple alkane consisting of two carbon atoms connected by a single bond, each bonded to three hydrogen atoms. Its structural simplicity makes it a key molecule in organic chemistry and industry. Ethane's combustion and substitution reactions demonstrate fundamental organic reactions, while its applications in producing ethylene highlight its industrial importance.
Understanding ethane’s formula and properties offers foundational knowledge for exploring more complex hydrocarbons and organic chemistry. From its molecular geometry, bonding, and physical characteristics to its industrial significance and safety considerations, ethane remains an essential compound in both academic study and practical applications.
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