Equação van der Waals
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
P + a/V²
About this calculator
The van der Waals equation is a fundamental formula in physical chemistry that describes the behavior of real gases. It adjusts the ideal gas equation to account for the interactions between molecules and the volume occupied by them. The proposed equation is (P + a/V²)(V - b) = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. The parameters a and b are specific to each gas and represent the intermolecular forces and the volume of the molecules, respectively.
The equation works by considering that the molecules of a gas are not point-like, but have a finite volume, and that there are attraction and repulsion forces between them. The term a/V² represents the additional pressure due to the attractive forces between molecules, while the term (V - b) corrects the available volume for the molecules to move, subtracting the volume occupied by the molecules themselves. This makes the equation more accurate for real gases, especially under conditions of high pressure and low temperature.
The van der Waals equation is particularly useful in cases where the ideal gas approximation is not sufficient, such as in industrial processes involving real gases, or in studies of thermodynamic properties of pure substances. However, care must be taken in choosing the values of a and b, as they can vary significantly between different gases and conditions.
It is worth noting that, although the van der Waals equation is a significant improvement over the ideal gas law, it is still a simplification and may not be accurate for all gases and conditions. For more precise applications, other more complex equations of state may be necessary.
Frequently asked questions
What are the parameters a and b in the van der Waals equation?
The parameters a and b are gas-specific constants. Parameter a represents the attractive forces between molecules, while parameter b represents the volume occupied by the molecules.
When should the van der Waals equation be used instead of the ideal gas law?
The van der Waals equation should be used when the conditions of pressure and temperature are such that the interactions between molecules and the volume of the molecules cannot be neglected, i.e., at high pressures and low temperatures.
Is the van der Waals equation accurate for all gases?
No, the van der Waals equation is an approximation and may not be accurate for all gases and conditions. It works well for many gases, but in specific cases, other equations of state may be necessary for greater precision.
How to determine the values of a and b for a specific gas?
The values of a and b are determined experimentally for each gas. They can be found in tables of physical properties of gases or obtained through laboratory measurements.
Can the van der Waals equation be used to predict thermodynamic properties?
Yes, the van der Waals equation can be used to predict thermodynamic properties such as vapor pressure, specific volume, and enthalpies of real gases.