Calculator Form
Example Data Table
Sample values below show how pressure, volume, and gas type affect energy density and total internal energy.
| Gas Type | Pressure (kPa) | Volume (m³) | Energy Density (kJ/m³) | Total Energy (kJ) | Relation |
|---|---|---|---|---|---|
| Monatomic | 101.325 | 0.50 | 151.988 | 75.994 | u = 1.5p |
| Diatomic | 200.000 | 0.20 | 500.000 | 100.000 | u = 2.5p |
| Polyatomic | 150.000 | 0.08 | 450.000 | 36.000 | u = 3.0p |
| Custom f = 4 | 250.000 | 0.12 | 500.000 | 60.000 | u = 2.0p |
Formula Used
u = U / VHere, u is energy density, U is total internal energy, and V is volume.
U = (f / 2) nRTThe factor f is the number of degrees of freedom.
p = nRT / VCombining this with internal energy gives
u = (f / 2) p.
p = (2 / f) × (U / V)For a monatomic ideal gas,
p = (2 / 3) × (U / V).
This page treats energy density as internal energy per unit volume. The selected gas model changes the factor between pressure and energy density.
How to Use This Calculator
- Select the calculation mode based on the data you already know.
- Choose a gas model, or enter custom degrees of freedom.
- Enter values with the correct units.
- Press the calculate button to view the result above the form.
- Use the graph to inspect how energy density scales with pressure.
- Download the result or example table as CSV or PDF if needed.
FAQs
1) What is energy density of a gas?
Energy density is the internal energy stored per unit volume. In symbols, it is u = U/V. It helps compare how much thermal energy a gas contains in a fixed space.
2) How do I express pressure p in terms of energy density U/V?
For an ideal gas with f degrees of freedom, p = (2/f) × (U/V). For a monatomic ideal gas, this becomes p = (2/3) × (U/V).
3) Why does gas type change the result?
Different gases can store energy in different modes. Monatomic gases mainly store translational energy, while diatomic and polyatomic gases can also store rotational energy. That changes the degrees-of-freedom factor.
4) What is the formula for monatomic ideal gases?
For a monatomic ideal gas, f = 3. So the internal energy is U = 3nRT/2, the energy density is u = 3p/2, and pressure becomes p = 2u/3.
5) Can I use this calculator with pressure and volume only?
Yes. In Pressure + Volume mode, the calculator uses the selected gas model to convert pressure into energy density, then multiplies by volume to get total internal energy.
6) What units are used for energy density?
The standard SI unit is joules per cubic meter, written as J/m³. This page also shows kJ/m³ and MJ/m³ for convenience when values become larger.
7) Does this calculator work for real gases?
It is designed for ideal-gas style calculations. Real gases at high pressure or very low temperature may deviate from these relations, so experimental data or advanced equations may be required.
8) Why is the graph useful?
The graph shows the linear relation between pressure and energy density for the selected gas model. It makes the proportional trend easier to inspect and compare with your computed point.