Difference Between Ethylene and Acetylene

Main Difference – Ethylene vs Acetylene

Ethylene and acetylene are hydrocarbons. They are very different in their chemical and physical properties. Ethylene can be found naturally in crude oil and natural gas; it is also found in plants as a plant hormone that causes the ripening of fruits. Acetylene is an alkyne. It is a linear molecule and is highly flammable. Therefore, it is used as a fuel. Acetylene is mainly produced by thermal cracking processes in refineries. The main difference between ethylene and acetylene is that ethylene is an alkene whereas acetylene is an alkyne.

Key Areas Covered

1. What is Ethylene
– Definition, Chemical Properties, Manufacturing, Uses
2. What is Acetylene
    – Definition, Chemical Properties, Manufacturing
3. Similarities Between Ethylene and Acetylene
      – Common Features
4. What is the Difference Between Ethylene and Acetylene
      – Comparison of Key Differences

Key Terms: Acetylene, Catalytic Cracking, Crude Oil, Ethane, Ethylene, Ethyne, Natural Gas, Thermal Cracking

What is Ethylene

Ethylene is the simplest alkene having the chemical formula H₂C=CH₂. It has two carbon atoms bonded to each other via a double bond. It is a colorless, flammable gas. The IUPAC name of ethylene is ethane. The molar mass of this compound is 28.05 g/mol. Its melting point is −169.2 °C and boiling point is −103.7 °C.

Difference Between Ethylene and Acetylene

Figure 1: Ball-and-Stick Model of Ethylene. Black – carbon atoms, White – hydrogen atoms

Ethylene has a sweet taste and odor. Natural sources of ethylene are crude oil and natural gas. Ethylene is used to make important compounds such as polymers; the polymers obtained by ethylene polymerization include poly(ethylene), poly(chloroethene) and poly(phenylethene). The other chemicals produced from ethylene include ethanol and epoxyethane.

Ethylene has two carbon atoms which are sp² hybridized. The carbon atoms are bonded via a sigma bond and a pi bond. Each carbon atom is bonded to 2 hydrogen atoms. It is a planar molecule. The geometry around one carbon atom is trigonal planar. The pi bond is responsible for the reactivity of the ethylene molecule.

Manufacturing Process

Ethylene is produced by cracking reactions. The fractions obtained from the distillation of natural gas and crude oil are subjected to three major cracking reactions as follows.

Steam cracking of ethane and propane from natural gas and crude oil
Steam cracking of naphtha from crude oil
Catalytic cracking of gas oil from crude oil

Uses of Ethylene

The major use of ethylene is as a monomer for the production of polymers. Polyethylene, which is used for packaging purposes, is one of the most widely used products of ethylene. Ethylene is also used to produce ethylene oxide, which is a major raw material used in the production of surfactants. In addition, ethylene is important as a plant hormone. It regulates the ripening of fruits, opening of flowers, etc.

What is Acetylene

Acetylene is the simplest alkyne having the chemical formula C₂H₂. It contains two carbon atoms bonded to each other via a triple bond. There are two pi bonds and one sigma bond between the carbon atoms. Each carbon atom is bonded to a hydrogen atom via a single bond. The molecule is planar, and the geometry around one carbon atom is linear.

Figure 2: Ball-and-Stick Model for Acetylene. Black – carbon atoms, white – hydrogen atoms

The molar mass of acetylene is 26.04 g/mol. Its IUPAC name is ethyne. It is a colorless flammable gas. Hence it is widely used as a gas. However, it is odorless (unlike ethylene). The melting point of acetylene is −80.8 °C, and the boiling point is −84 °C.

At atmospheric pressure, acetylene cannot exist as a liquid. Therefore, it actually does not have a melting point. Hence, the triple point of acetylene is considered as its melting point. The triple point of a substance is the temperature at which all three phases of matter exist in thermodynamic equilibrium. At temperatures below the triple point, solid acetylene can undergo sublimation, where solid acetylene directly converts into its vapor phase.

Manufacturing of Acetylene

The simplest process to produce acetylene is to react calcium carbide with water. It gives acetylene gas and calcium carbonate slurry (hydrated lime). In industrial needs, two main methods are used to produce acetylene.

Chemical reaction process, which is done at room temperature
Thermal cracking process, which occurs at extremely high temperatures

The chemical reaction process is the production of acetylene from calcium carbide as mentioned above. The thermal cracking process is a method that includes cracking or breaking of bonds and rebinding to get a new compound.

Similarities Between Ethylene and Acetylene

Both are hydrocarbon compounds.
Both are colorless gases at room temperature.
Both are highly flammable.
Both are composed of C-H bonds.
Both are unsaturated compounds.
Both are planar structures.

Definition

Ethylene: Ethylene is the simplest alkene having the chemical formula H₂C=CH₂.

Acetylene: Acetylene is the simplest alkyne having the chemical formula C₂H₂.

Chemical Bonding between Carbon Atoms

Ethylene: There is a double bond between two carbon atoms in ethylene.

Acetylene: There is a triple bond between two carbon atoms in acetylene.

Molar Mass

Ethylene: The molar mass of ethylene is 28.05 g/mol.

Acetylene: The molar mass of acetylene is 26.04 g/mol.

IUPAC Name

Ethylene: IUPAC name of ethylene is ethane.

Acetylene: IUPAC name of acetylene is ethyne.

Melting Point and Boiling Point

Ethylene: The melting point of ethylene is −169.2 °C, and the boiling point is −103.7 °C.

Acetylene: The melting point of acetylene is −80.8 °C, and the boiling point is −84 °C.

Odor

Ethylene: Ethylene has a sweet odor.

Acetylene: Acetylene is odorless.

Geometry

Ethylene: The geometry around one carbon atom is linear in acetylene.

Acetylene: The geometry around one carbon atom is trigonal planar in ethylene.

Conclusion

Both ethylene and acetylene are hydrocarbon compounds. They are the simplest alkene and alkyne, respectively. Ethylene can be found naturally, but acetylene is made using different technological methods. The main difference between ethylene and acetylene is that ethylene is an alkene whereas acetylene is an alkyne.

Reference:

1. Lazonby, John. “Ethene (Ethylene).” The Essential Chemical Industry online, Available here.
2. Carey, Francis A. “Ethylene.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 10 Dec. 2014, Available here.
3. “Acetylene.” How Products Are Made, Available here.

Image Courtesy:

1. “Ethylene-3D-balls” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
2. “Acetylene-CRC-IR-3D-balls” By Ben Mills – Own work (Public Domain) via Commons Wikimedia