Alkene
An alkene is an unsaturated hydrocarbon containing at least one carbon–carbon double bond (C=C), with the simplest members following the general formula CₙH₂ⁿ. The double bond consists of a sigma bond and a pi bond, making alkenes more reactive than alkanes and susceptible to addition reactions. Alkenes are industrially vital — ethylene alone is the most-produced organic chemical worldwide, used to make polyethylene plastic.
Key Formula
CnH(2n)
LaTeX: C_nH_{2n}
| Symbol | Meaning | Unit |
|---|---|---|
| n | number of carbon atoms (n ≥ 2 for acyclic alkenes) | dimensionless |
Worked Example
Problem
Ethylene (C₂H₄) undergoes hydrogenation: C₂H₄ + H₂ → C₂H₆. If 28 g of ethylene reacts completely with excess H₂, calculate the mass of ethane produced.
Solution
Step 1: Molar mass of C₂H₄ = 2(12.01) + 4(1.008) = 28.05 g/mol. Step 2: Moles of C₂H₄ = 28 g ÷ 28.05 g/mol ≈ 0.998 mol. Step 3: Mole ratio C₂H₄ : C₂H₆ = 1:1, so moles of C₂H₆ = 0.998 mol. Step 4: Molar mass of C₂H₆ = 30.07 g/mol. Step 5: Mass of ethane = 0.998 × 30.07 = 30.01 g.
Answer
30.01 g of ethane (C₂H₆)
Common Alkenes and Their Industrial Uses
| Name | Formula | Double Bond Position | Industrial Use | Boiling Point (°C) |
|---|---|---|---|---|
| Ethylene | C₂H₄ | C1=C2 | Polyethylene production | −104 |
| Propylene | C₃H₆ | C1=C2 | Polypropylene, acetone | −47.6 |
| 1-Butene | C₄H₈ | C1=C2 | Copolymer additive | −6.3 |
| 2-Butene | C₄H₈ | C2=C3 | Fuel blending | 0.9 |
| Styrene | C₈H₈ | Vinyl group | Polystyrene, ABS | 145 |
Interactive Tools
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Related Terms
Alkane
An alkane is a saturated hydrocarbon in which all carbon atoms are connected by single covalent bonds, giving the general formula CₙH₂ⁿ₊₂. Because alkanes contain no double or triple bonds, they are chemically less reactive than other hydrocarbons and are described as "paraffins" in the petroleum industry. They are the principal components of natural gas and crude oil, making them critical energy sources.
Alkyne
An alkyne is an unsaturated hydrocarbon that contains at least one carbon–carbon triple bond (C≡C), with the simplest acyclic alkynes following the general formula CₙH₂ⁿ₋₂. The triple bond comprises one sigma and two pi bonds, making alkynes highly reactive and capable of two successive addition reactions. The simplest alkyne, acetylene (ethyne), is widely used in welding torches because its combustion with oxygen produces a flame exceeding 3,500 °C.
Hydrocarbon
A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon atoms, forming the simplest class of organic molecules. Hydrocarbons are classified by their bonding: saturated (single bonds only) or unsaturated (containing double or triple bonds). They are the primary constituents of fossil fuels and serve as feedstocks for the petrochemical industry.
From French "alcène," derived by Charles-Adolphe Wurtz (1850s) from "alcool" (alcohol) + Greek "-ene" (denoting unsaturation). The IUPAC "-ene" suffix was standardized in 1892 to indicate a carbon–carbon double bond.