Calculator Inputs
Formula used
For a van der Waals fluid, the equation of state is:
P = RT/(V - b) - a/V^2
The spinodal line is the mechanical stability limit:
(dP/dV)_T = 0
Substitution and algebra yield a cubic in V:
RT*V^3 - 2a*V^2 + 4ab*V - 2ab^2 = 0
This calculator solves that cubic, filters physical roots with V > b, and reports pressures at each spinodal volume.
How to use this calculator
- Enter the temperature and choose its unit.
- Provide van der Waals parameters a and b.
- Set R so units remain consistent.
- Select output units for pressure and volume.
- Press Calculate to show results above the form.
- Use CSV or PDF buttons to export results.
Example data table
| Case (example) | T (K) | a (Pa*m^6/mol^2) | b (m^3/mol) | Expected behavior |
|---|---|---|---|---|
| CO2 (illustrative) | 280 | 0.364 | 4.27e-5 | Two spinodal volumes when T < Tc |
| Generic fluid | 350 | 0.300 | 3.80e-5 | No roots if T is at or above Tc |
Example parameters are for demonstration only. Use substance-specific values from a reliable source.