Calculator Inputs
Enter gas constants and state variables using liters, bar, kelvin, and moles.
Example Data Table
These sample rows help demonstrate typical inputs and how corrected pressure can differ from ideal pressure.
| Gas | a (L²·bar/mol²) | b (L/mol) | n (mol) | T (K) | V (L) | Ideal P (bar) | Real P (bar) | Z |
|---|---|---|---|---|---|---|---|---|
| Carbon Dioxide | 3.5920 | 0.0427 | 1.0000 | 300.0000 | 10.0000 | 2.4942 | 2.4690 | 0.9899 |
| Nitrogen | 1.3900 | 0.0391 | 1.0000 | 320.0000 | 8.0000 | 3.3256 | 3.3013 | 0.9927 |
| Methane | 2.2530 | 0.0428 | 2.0000 | 310.0000 | 12.0000 | 4.2956 | 4.2358 | 0.9861 |
Formula Used
\( P_{\text{ideal}} = \dfrac{nRT}{V} \)
\( P_{\text{real}} = \dfrac{nRT}{V - nb} - a\left(\dfrac{n}{V}\right)^2 \)
\( Z = \dfrac{PV}{nRT} \)
\( \%\,\text{Deviation} = \dfrac{P_{\text{real}} - P_{\text{ideal}}}{P_{\text{ideal}}} \times 100 \)
Meaning of constants: a adjusts for intermolecular attraction, while b corrects for finite molecular size.
This page uses L·bar·mol⁻¹·K⁻¹ units for the gas constant, so enter volume in liters, pressure in bar, temperature in kelvin, and amount in moles.
How to Use This Calculator
- Select a preset gas or choose custom values.
- Enter the van der Waals constants a and b.
- Provide moles, temperature, and volume in the displayed units.
- Optionally enter measured pressure to compare an observed state.
- Optionally enter a custom compressibility factor Z for alternate correction estimates.
- Add molar mass if you also want mass and density outputs.
- Press Calculate Real Gas Correction.
- Review the summary, full metric table, and Plotly pressure graph, then export CSV or PDF if needed.
Frequently Asked Questions
1) What does real gas correction mean?
It adjusts ideal-gas calculations for finite molecular size and intermolecular attraction. These effects become more important at higher pressures, lower volumes, and lower temperatures.
2) Why does the calculator use van der Waals constants?
The constants a and b provide a practical first-level correction. They account for attraction between molecules and excluded volume caused by molecular size.
3) What does the Z factor show?
The compressibility factor compares real behavior with ideal behavior. Z near 1 means the gas is close to ideal. Larger departures show stronger nonideal effects.
4) Why can real pressure be lower than ideal pressure?
Attractive intermolecular forces pull molecules inward and reduce wall impacts. That can lower measured pressure below the ideal prediction at the same temperature, volume, and amount.
5) Why can real pressure be higher than ideal pressure?
At very small volumes, the excluded-volume correction becomes strong. Molecules have less free space, so the repulsive term can dominate and drive pressure above the ideal estimate.
6) Can I use this for liquids or phase-change regions?
No. This calculator is intended for gas-state estimates. Near condensation, critical conditions, or multiphase regions, more advanced equations of state are usually needed.
7) Which units should I enter?
Use liters for volume, bar for pressure, kelvin for temperature, moles for amount, L²·bar/mol² for a, and L/mol for b. Keep units consistent throughout.
8) What do CSV and PDF exports include?
They include your entered values, computed metrics, and a curve table for the graph. The PDF also places the Plotly chart into a report-style output.