OMEGA

This function returns a pure component’s acentric factor from curated data sources using its CAS number.

The acentric factor quantifies non-sphericity and deviation from simple-fluid behavior and is widely used in cubic equation-of-state parameterization.

\omega = -\log_{10}\left(P_r^{sat}(T_r=0.7)\right)-1

Excel Usage

=OMEGA(CASRN, method)

• CASRN (str, required): CAS Registry Number for the target chemical (-).
• method (str, optional, default: null): Optional data source method name; leave empty for automatic selection (-).

Returns (float): Acentric factor of the specified compound (-).

Example 1: Acentric factor of water

Inputs:

CASRN
7732-18-5

Excel formula:

=OMEGA("7732-18-5")

Expected output:

0.3443

Example 2: Acentric factor of ethanol

Inputs:

CASRN
64-17-5

Excel formula:

=OMEGA("64-17-5")

Expected output:

0.646

Example 3: Acentric factor of methane

Inputs:

CASRN
74-82-8

Excel formula:

=OMEGA("74-82-8")

Expected output:

0.01142

Example 4: Acentric factor of benzene

Inputs:

CASRN
71-43-2

Excel formula:

=OMEGA("71-43-2")

Expected output:

0.211

Python Code

Show Code

from chemicals.acentric import omega as chemicals_omega

def omega(CASRN, method=None):
    """
    Retrieve the acentric factor of a chemical by CAS number.

    See: https://chemicals.readthedocs.io/chemicals.acentric.html

    This example function is provided as-is without any representation of accuracy.

    Args:
        CASRN (str): CAS Registry Number for the target chemical (-).
        method (str, optional): Optional data source method name; leave empty for automatic selection (-). Default is None.

    Returns:
        float: Acentric factor of the specified compound (-).
    """
    try:
        value = chemicals_omega(CASRN=CASRN, method=method)
        if value is None:
            return "Error: Acentric factor data is not available for the provided CASRN"
        return value
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

CASRN *

CAS Registry Number for the target chemical (-).

method

Optional data source method name; leave empty for automatic selection (-).