van der Waals' Equation
Definition and meaning of van der Waals' Equation in chemistry.
The van der Waals equation is a thermodynamic equation of state that successfully modifies the ideal gas law to accurately account for the non-ideal behavior of real gases.
In more detail
The foundational ideal gas law incorrectly assumes that gas particles have zero volume and do not exert any intermolecular forces upon one another. Johannes Diderik van der Waals introduced two specific empirical correction factors into his equation to explicitly address these flawed assumptions. The parameter 'a' corrects for the attractive forces acting between gas molecules, which marginally reduces the total pressure exerted on the container walls, while the parameter 'b' accounts for the finite physical volume occupied by the gas molecules themselves. This expanded equation provides a much more accurate mathematical description of gas behavior, especially when dealing with gases at high pressures and low temperatures.
Key facts
| Field | Physical Chemistry |
|---|---|
| Parameter a | Corrects for intermolecular attractive forces |
| Parameter b | Corrects for molecular particle volume |
For carbon dioxide gas, the specific van der Waals constants 'a' and 'b' are used to calculate the real pressure of the gas when compressed in a high-pressure cylinder, which yields a notably lower predicted pressure than the basic ideal gas law.
Frequently asked questions
When is the van der Waals equation most practically useful for chemists?
It is most useful for describing gases under extreme conditions where they deviate significantly from ideal behavior, such as very high pressures and low temperatures close to their natural liquefaction point.