What is Fugacity?

In chemical thermodynamics, fugacity is a measure of the chemical potential of a substance. For an ideal gas, the pressure is a direct representation of its activity. However, in real-world applications where gases do not behave ideally due to intermolecular forces, fugacity is used as an "effective" partial pressure. It represents the tendency of a substance to prefer one phase (liquid, solid, or gas) over another.

How the Fugacity Formula Works

The relationship between fugacity (f), the fugacity coefficient (φ), and the total pressure (P) is expressed by the fundamental formula:

f = φ × P

Where:

• f: The Fugacity (expressed in the same units as pressure).
• φ (Phi): The fugacity coefficient. For an ideal gas, φ = 1, meaning fugacity equals pressure. For real gases, φ may be greater or less than 1 depending on the temperature and pressure.
• P: The observed system pressure.

How to Use This Fugacity Calculator

Using our online tool is simple and requires only a few inputs:

1. Input Pressure: Enter the absolute pressure of your system.
2. Select Unit: Choose the pressure unit (atm, bar, kPa, or PSI) to ensure consistency.
3. Enter Coefficient: Provide the fugacity coefficient (φ). This is usually derived from Equations of State (EOS) like Peng-Robinson or Redlich-Kwong for specific temperatures.
4. Get Results: Click calculate to instantly see the effective pressure exerted by the real gas.

Frequently Asked Questions (FAQ)

Why is fugacity important?

Fugacity is crucial for calculating phase equilibrium. In industries like oil and gas or chemical processing, knowing the fugacity allows engineers to predict how components will distribute between liquid and vapor phases in separators and distillation columns.

Can fugacity be greater than pressure?

Yes. While at high pressures attractive forces often make fugacity lower than pressure (φ < 1), at extremely high pressures where repulsive forces dominate, the fugacity coefficient can exceed 1, making fugacity greater than the observed pressure.

What is the unit of fugacity?

Fugacity has the same units as pressure (e.g., Pascal, Bar, or Atmospheres).