Liquid Ethylene Density Calculator

What is Ethylene?

Ethylene (IUPAC name: ethene) is the simplest alkene, with the molecular formula C₂H₄ and the structural formula H₂C=CH₂. It is a colorless, flammable gas with a faintly sweet odor that is produced on an enormous scale industrially and is also a naturally occurring plant hormone that regulates fruit ripening, flower wilting, and leaf fall.

The ethylene molecule is planar, with each carbon atom adopting sp² hybridization. The carbon-carbon double bond consists of one sigma bond and one pi bond, giving a bond length of 1.339 angstroms, which is shorter than the typical C-C single bond length of 1.54 angstroms. The H-C-H bond angle is approximately 117.4 degrees, while the H-C=C bond angle is approximately 121.3 degrees, both close to the ideal trigonal planar angle of 120 degrees.

All six atoms in ethylene lie in the same plane because of the rigidity imposed by the pi bond, which prevents free rotation around the C=C axis. This planarity is essential for understanding ethylene's reactivity: the exposed pi electrons above and below the molecular plane make ethylene highly susceptible to electrophilic addition reactions.

Physical Properties of Ethylene

Ethylene has a relatively low boiling point and low critical temperature, reflecting its small molecular size and weak intermolecular van der Waals forces. Below is a summary of its most important physical constants:

Molecular weight: 28.054 g/mol
Melting point: -169.15°C (104.00 K)
Normal boiling point: -103.77°C (169.38 K) at 1 atm
Critical temperature (Tc): 282.34 K (9.19°C)
Critical pressure (Pc): 5.042 MPa (49.77 atm)
Critical density: 214.24 kg/m³
Acentric factor: 0.0862
Triple point: 104.00 K at 0.00012 MPa

Because ethylene's critical temperature is only 9.19°C, liquid ethylene can only exist at moderate pressures near room temperature. At atmospheric pressure, ethylene is a liquid only below its boiling point of -103.77°C. Storage and transportation of liquid ethylene therefore require either very low temperatures (cryogenic conditions) or elevated pressures, or a combination of both.

How Does Temperature Affect Ethylene Density?

The density of liquid ethylene decreases as temperature increases. This behavior is typical of most liquids and arises because thermal energy causes increased molecular motion and intermolecular spacing. As molecules vibrate and translate more vigorously at higher temperatures, they occupy a larger effective volume, reducing the number of molecules per unit volume and hence the density.

At the lowest temperatures near the melting point (104 K), liquid ethylene is at its densest, approximately 655 kg/m³. As the temperature rises toward the normal boiling point (169.38 K), the density drops to about 568 kg/m³. The decline continues through intermediate temperatures, and as the liquid approaches its critical temperature of 282.34 K, the density decreases sharply to the critical density of approximately 214 kg/m³.

Near the critical point, the distinction between liquid and vapor phases vanishes. The density of the liquid and vapor converge, and at the critical point itself, there is only a single supercritical phase. This is why the density curve shows an increasingly steep drop as it approaches the critical temperature.

Key insight: The relationship between temperature and liquid density is nonlinear. The density decreases slowly at low temperatures but accelerates as the critical point is approached. This is captured mathematically by the Rackett equation's (2/7) power exponent.

Liquid Ethylene Density Formula

This calculator uses the Modified Rackett Equation, which is widely regarded as one of the most accurate correlations for predicting saturated liquid densities of pure compounds. The equation is:

ρ = ρ_c × Z_RA^{−(1 − T/T_c)^2/7}

Where:

ρ = saturated liquid density (kg/m³)
ρ_c = critical density = 214.24 kg/m³ for ethylene
Z_RA = Rackett compressibility factor = 0.2812 for ethylene
T = temperature in Kelvin
T_c = critical temperature = 282.34 K

The exponent −(1 − T/T_c)^2/7 captures the characteristic shape of the liquid density curve. At low temperatures where T/T_c is small, the exponent is large and negative, producing a high density. As T approaches T_c, the exponent approaches zero, and the density approaches ρ_c.

For subcooled liquids (liquid under pressure above the saturation pressure at a given temperature), the density is slightly higher than the saturated value. A common correction uses the Tait equation or a simple compressibility factor. This calculator applies a small pressure correction when the input pressure exceeds the saturation pressure.

Ethylene Density Table

The following table presents reference density values for saturated liquid ethylene at various temperatures. These values are computed using the Modified Rackett Equation and are consistent with published thermodynamic data from NIST and engineering references.

Temperature (°C)	Temperature (K)	Density (kg/m³)	Density (g/cm³)	Density (lb/ft³)

Uses of Ethylene

Ethylene is the most widely produced organic compound in the world, with global production exceeding 200 million metric tons per year. It serves as the foundational building block for a vast array of chemical products:

Polyethylene production: The largest use of ethylene is in the manufacture of polyethylene (PE), the world's most common plastic. Low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are used in packaging films, containers, pipes, and countless other applications. Linear low-density polyethylene (LLDPE) is another important variant.
Ethylene oxide: Ethylene is oxidized to produce ethylene oxide, a key intermediate for making ethylene glycol (antifreeze and polyester fiber raw material), surfactants, and other chemicals.
Ethylene glycol: Produced from ethylene oxide, ethylene glycol is essential as an engine coolant/antifreeze and as a precursor for polyethylene terephthalate (PET), used in plastic bottles and polyester textiles.
Vinyl chloride monomer (VCM): Ethylene reacts with chlorine to eventually produce vinyl chloride, the monomer for polyvinyl chloride (PVC), one of the most versatile plastics.
Styrene: Ethylene is combined with benzene to form ethylbenzene, which is dehydrogenated to styrene, the monomer for polystyrene and synthetic rubber.
Fruit ripening agent: Ethylene is a natural plant hormone. It is applied commercially to accelerate the ripening of bananas, tomatoes, avocados, and other climacteric fruits during transportation and storage.
Welding gas: Ethylene is sometimes used as a fuel gas in oxyethylene welding and cutting operations.

Safety Considerations

Ethylene is a flammable gas that requires careful handling and storage. Understanding its hazard properties is essential for safe operations:

Flammability: Ethylene is extremely flammable. Its lower explosive limit (LEL) is 2.7% by volume in air, and its upper explosive limit (UEL) is 36%. This very wide flammable range means that leaks can easily create explosive atmospheres.
Autoignition temperature: 490°C (914°F). Ethylene can ignite spontaneously if exposed to surfaces above this temperature.
Toxicity: Ethylene has low acute toxicity. It acts primarily as an asphyxiant at very high concentrations by displacing oxygen. At concentrations above 50,000 ppm, it can cause drowsiness and loss of consciousness.
Cryogenic hazards: Liquid ethylene is extremely cold (-103.77°C at atmospheric pressure). Contact with skin or eyes can cause severe frostbite. Equipment and piping must be designed for cryogenic service.
Storage: Liquid ethylene is stored in insulated cryogenic tanks at near-atmospheric pressure or in pressurized vessels at ambient temperature. Pressure relief systems are mandatory to prevent vessel rupture from thermal expansion or boil-off.
Ventilation: Because ethylene is heavier than air at ambient conditions (vapor density about 0.97 relative to air), adequate ventilation is necessary to prevent accumulation in low-lying areas. Gas detection systems should be installed in areas where leaks may occur.

Safety summary: Always handle ethylene in well-ventilated areas, use appropriate PPE (including cryogenic gloves for liquid ethylene), install gas detection and fire suppression systems, and follow all applicable codes and standards (e.g., NFPA 55, ASME B31.3).

How to Use This Calculator

Follow these steps to calculate the density of liquid ethylene:

Enter the temperature: Type the temperature into the input field or use the slider for quick adjustments. The default value is the normal boiling point (-103.77°C). You can select your preferred unit (°C, °F, or K) from the dropdown.
Set the pressure (optional): If you are working with subcooled liquid ethylene (liquid under pressure above saturation), enter the pressure. The default is 1 atm. For saturated liquid calculations, the pressure input does not significantly affect the result.
Choose the output unit: Select your preferred density unit from the dropdown: kg/m³, g/cm³, g/L, or lb/ft³.
Click "Calculate Density": The result will appear immediately below the button, along with automatic conversions to all supported units.
Use the mass/volume converter: After calculating density, you can enter a volume to find the corresponding mass, or enter a mass to find the corresponding volume. This is useful for sizing storage vessels or calculating how much ethylene a container holds.
Review the chart: The interactive density chart below the calculator visualizes how density changes across the entire liquid temperature range, with your calculated point highlighted.

Valid temperature range: from the melting point at -169.15°C (104 K) to the critical temperature at 9.19°C (282.34 K). Temperatures outside this range will produce an error message since ethylene cannot exist as a liquid outside these bounds at saturation conditions.

Frequently Asked Questions

At the normal boiling point of -103.77°C (169.38 K) and 1 atmosphere of pressure, the density of saturated liquid ethylene is approximately 568 kg/m³ (0.568 g/cm³). This means liquid ethylene is significantly less dense than water (1000 kg/m³) and is comparable in density to light hydrocarbons like liquid propane.

Not at atmospheric pressure. The critical temperature of ethylene is 282.34 K (9.19°C), which means that above this temperature, no amount of pressure can liquefy ethylene. At temperatures between the boiling point and the critical temperature, ethylene can be liquefied by applying sufficient pressure. For example, at 0°C, ethylene can be liquefied at pressures above approximately 4.0 MPa. At typical room temperatures of 20-25°C, ethylene is above its critical temperature and exists only as a supercritical fluid regardless of pressure.

The Modified Rackett Equation is a widely used thermodynamic correlation for predicting the molar volume (and thus density) of saturated liquids. It was developed by Spencer and Danner as an improvement to the original Rackett equation. For ethylene, the equation is accurate to within approximately 1-2% across the entire liquid range from the melting point to the critical point. The key parameter is the Rackett compressibility factor Z_RA, which is specific to each compound and is typically regressed from experimental data. For ethylene, Z_RA = 0.2812.

As temperature increases, ethylene molecules gain kinetic energy and vibrate and move more rapidly. This increased molecular motion causes the average distance between molecules to grow, which means the same mass of ethylene occupies a larger volume. Since density is mass per unit volume, the density decreases. Near the critical temperature, the intermolecular attractive forces become insufficient to maintain the liquid structure, and the density drops rapidly as the liquid and vapor phases merge into a single supercritical phase.

Liquid ethylene is stored and transported in two main ways. For large-scale operations, it is kept in fully refrigerated atmospheric-pressure tanks at approximately -104°C. These are large, insulated vessels similar to those used for liquefied natural gas (LNG). For smaller quantities or pipeline transportation, ethylene may be stored under pressure at higher temperatures in pressurized spheres or bullets. Ethylene pipelines operate throughout major petrochemical regions, particularly along the U.S. Gulf Coast and in Western Europe. The choice between refrigerated and pressurized storage depends on volume, cost, and operational requirements.

Despite their similar-sounding names, ethylene (C₂H₄) and ethanol (C₂H₅OH) are very different compounds. Ethylene is a two-carbon unsaturated hydrocarbon (an alkene) that is a gas at room temperature. Ethanol is a two-carbon alcohol that is a liquid at room temperature, commonly known as drinking alcohol. Ethanol has a much higher boiling point (78.37°C vs. -103.77°C) because of hydrogen bonding between its hydroxyl (-OH) groups. Industrially, ethanol can be produced from ethylene by catalytic hydration (adding water across the double bond).

The most common units for liquid density are:

kg/m³ (SI unit) - Kilograms per cubic meter. This is the standard in most scientific and engineering contexts.
g/cm³ - Grams per cubic centimeter. To convert from kg/m³, divide by 1000. For example, 568 kg/m³ = 0.568 g/cm³.
g/L - Grams per liter. Numerically identical to kg/m³. So 568 kg/m³ = 568 g/L.
lb/ft³ - Pounds per cubic foot. To convert from kg/m³, multiply by 0.062428. For example, 568 kg/m³ = 35.46 lb/ft³.