Ideal Gas
Definition and meaning of Ideal Gas in chemistry.
An ideal gas is a theoretical gas whose particles are treated as point masses with negligible volume and no intermolecular forces, so its pressure, volume, temperature, and amount are related exactly by the ideal gas law, PV = nRT.
In more detail
This model comes from kinetic molecular theory, which assumes gas particles move randomly, collide elastically, and interact only during collisions. No real gas fits these assumptions perfectly, but most gases approximate ideal behavior closely at low pressure and high temperature, where particles are far apart and interactions become negligible. Deviations grow at high pressure or low temperature, where molecular volume and attractive forces (accounted for in the van der Waals equation) become significant. The ideal gas law remains a workhorse approximation for stoichiometry, gas density, and molar mass calculations.
Key facts
| Field | Physical Chemistry |
|---|---|
| Governing equation | PV = nRT |
| Gas constant (R) | 8.314 J/(mol·K) |
| Key assumptions | Negligible particle volume; no intermolecular forces |
Using PV = nRT, one mole of an ideal gas at 0 degrees C (273.15 K) and 1 atm occupies 22.4 L, a value used as a standard reference molar volume in many gas-law problems.
Frequently asked questions
Do any real gases behave ideally?
No gas is perfectly ideal, but gases like helium and hydrogen behave very close to ideal at ordinary temperatures and pressures because their small, nonpolar molecules have weak intermolecular attractions.
Why do real gases deviate from ideal behavior?
Real gas molecules have finite volume and experience intermolecular attractions, both ignored in the ideal gas model; these effects become significant at high pressure and low temperature, where molecules are forced close together.