How this calculation works
The Ideal Gas Law Calculator solves the thermodynamic equation of state (PV = nRT) for volume, pressure, moles, or temperature of ideal gases at any physical pressure and thermal condition.
Mathematical formula and logic
V = (n × R × T) / P, where R = 0.082057 L·atm/(mol·K) (or 8.31446 J/(mol·K)), and T is absolute temperature in Kelvin (T_K = T_C + 273.15).
Worked example
1.0 mole of ideal gas at 1.0 atm pressure and 25°C (298.15 K) occupies V = (1.0 × 0.082057 × 298.15) / 1.0 = 24.46 Liters.
Calculation assumptions
- NIST Universal Gas Constant R = 0.0820574 L·atm/(mol·K).
- Gas particles behave ideally with negligible volume and zero intermolecular attractive forces.
Frequently asked questions
What is the molar volume of an ideal gas at STP?
At Standard Temperature and Pressure (STP: 0°C / 273.15 K and 1 atm), exactly 1 mole of any ideal gas occupies 22.414 Liters.
What is the molar volume of an ideal gas at room temperature (SATP)?
At Standard Ambient Temperature and Pressure (SATP: 25°C / 298.15 K and 1 bar / 0.987 atm), 1 mole of ideal gas occupies 24.789 Liters (approx 24.46 L at 1 atm).
Why must temperature always be in Kelvin for gas laws?
The Kelvin scale is absolute; zero Kelvin represents absolute zero (zero thermal kinetic energy). Using Celsius or Fahrenheit would produce invalid mathematical zeros or negative gas volumes.
When do real gases deviate from ideal behavior?
Real gases deviate from ideal behavior at very high pressures (where particle volume becomes significant) and very low temperatures near condensation points (where intermolecular van der Waals forces take over).
What is the van der Waals equation?
The van der Waals equation modifies the ideal gas law with constants 'a' (intermolecular attraction) and 'b' (particle molecular volume) to accurately model real gas thermodynamics.
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