What Is Ethylene?
Ethylene, also known as ethene, is the simplest alkene—a hydrocarbon containing a carbon–carbon double bond. Its molecular formula is C₂H₄, with the structural representation H₂C=CH₂ showing the characteristic double bond between the two carbon atoms.
Plants naturally synthesise ethylene as a plant hormone regulating fruit ripening and other developmental processes. In industry, it serves as the starting material for producing polyethylene, ethylene oxide, ethylene dichloride, and ethylbenzene through electrophilic addition reactions.
At standard atmospheric pressure (1 bar), ethylene transitions between solid and gas phases at fixed temperatures:
- Melting point: −169.2 °C
- Boiling point: −103.7 °C
Between these extremes, ethylene exists as a liquid. Pressurising the gas expands this liquid range, allowing storage and handling at higher temperatures or lower pressures than otherwise possible.
Density Calculation from Mass and Volume
The most direct method to determine liquid ethylene density involves measuring its mass and the volume it occupies. This experimental approach requires careful handling owing to ethylene's low boiling point and requires appropriate cryogenic equipment.
ρ = m / V
ρ— Density of liquid ethylene (kg/m³ or g/cm³)m— Mass of liquid ethylene (kg or g)V— Volume occupied by liquid ethylene (m³ or cm³)
Thermodynamic Density Lookup
Beyond simple mass-to-volume calculations, liquid ethylene density varies significantly with both temperature and absolute pressure. Industrial and research applications often require density values at non-standard conditions.
This calculator includes a thermodynamic database allowing direct lookup of liquid ethylene density at specified temperature and pressure combinations. Enter your operating conditions, and the tool retrieves the corresponding density without requiring experimental measurements.
Pressure must be absolute pressure (bar, Pa, atm), not gauge pressure. Temperature inputs should span the liquid region; values outside the phase envelope will not return valid results, as ethylene cannot exist as a liquid under those conditions.
Water Solubility and Industrial Properties
Ethylene shows limited but measurable solubility in water—approximately 131 mg per litre at 25 °C, increasing to roughly 250 mg/L at 0 °C. This modest aqueous solubility reflects its nonpolar nature and has implications for storage container design and contamination management.
The C–C double bond length is 133.9 picometres, while C–H bonds measure 108.7 pm. The H–C–H and C–C–H bond angles average 121.3°, characteristics that define its reactivity and physical behaviour. These molecular parameters underpin all density calculations and phase behaviour across different conditions.
Practical Considerations for Density Work
When calculating or measuring liquid ethylene density, several factors warrant attention to ensure accuracy and safety.
- Cryogenic handling equipment required — Liquid ethylene exists only below −103.7 °C at standard pressure. Measuring mass and volume demands insulated containers, thermocouples, and pressure gauges rated for cryogenic service. Never attempt measurement in standard glassware or aluminium vessels.
- Absolute pressure matters — The density lookup feature requires absolute pressure values. Gauge pressure readings (common on industrial systems) must be converted by adding atmospheric pressure (≈1.013 bar). Confusing the two introduces significant errors in thermodynamic lookups.
- Phase boundary sensitivity — Liquid ethylene exists in a narrow envelope bounded by melting and boiling curves. Small temperature or pressure changes near the saturation line can shift ethylene between liquid and gas phases. Always confirm your operating point lies within the two-phase region before relying on calculated density values.
- Contamination and purity effects — Industrial ethylene often contains trace ethane, propane, or other alkenes that subtly shift density. Laboratory-grade or high-purity ethylene yields more reliable results. Document the purity specification when comparing measured versus calculated densities.