Van der Waals

Definition

van der Waals forces are weak intermolecular attractive forces that arise between neutral molecules, contributing to the behavior of real gases and deviations from the ideal gas law.

5 Must Know Facts For Your Next Test

1. van der Waals forces are attractive forces that arise from temporary or induced dipole moments in neutral molecules, in addition to permanent dipole moments.
2. The van der Waals equation of state is a modified version of the ideal gas law that accounts for the finite volume of gas molecules and the attractive van der Waals forces between them.
3. The van der Waals equation is used to describe the behavior of real gases, which deviate from the ideal gas law at high pressures and low temperatures.
4. The van der Waals constants, $a$ and $b$, are used in the van der Waals equation to quantify the attractive forces and the finite volume of the gas molecules, respectively.
5. The inclusion of van der Waals forces in the equation of state leads to a more accurate description of the heat capacity of real gases, particularly at high pressures and low temperatures.

Review Questions

• Explain how the van der Waals forces influence the behavior of real gases compared to ideal gases.
  • The van der Waals forces are attractive intermolecular forces that arise between neutral gas molecules. These forces cause real gases to deviate from the ideal gas behavior, particularly at high pressures and low temperatures. The van der Waals equation of state accounts for the finite volume of gas molecules and the attractive van der Waals forces, leading to a more accurate description of the behavior of real gases compared to the ideal gas law. The van der Waals forces result in real gases exhibiting higher pressures and lower volumes than predicted by the ideal gas law.
• Describe the role of the van der Waals constants, $a$ and $b$, in the van der Waals equation of state.
  • The van der Waals constants, $a$ and $b$, are used in the van der Waals equation of state to account for the deviations from ideal gas behavior. The constant $a$ represents the attractive forces between gas molecules, while the constant $b$ represents the finite volume of the gas molecules. The values of these constants are specific to each gas and are determined experimentally. The inclusion of these constants in the van der Waals equation allows for a more accurate description of the pressure-volume-temperature relationships of real gases, particularly at high pressures and low temperatures where the effects of intermolecular forces and molecular volume become significant.
• Explain how the van der Waals forces affect the heat capacity of real gases compared to ideal gases.
  • The van der Waals forces have a significant impact on the heat capacity of real gases, particularly at high pressures and low temperatures. In an ideal gas, the heat capacity is constant and independent of pressure and temperature. However, in a real gas, the van der Waals forces introduce additional degrees of freedom for the gas molecules, which can store and release energy. This results in a pressure- and temperature-dependent heat capacity that deviates from the constant value observed in ideal gases. The inclusion of van der Waals forces in the equation of state leads to a more accurate description of the heat capacity of real gases, allowing for better predictions of their thermodynamic behavior in various applications.

Related terms

Intermolecular Forces: The attractive or repulsive forces that exist between neighboring molecules, which influence the physical properties and behavior of substances.

Ideal Gas Law: The equation of state that describes the relationship between the pressure, volume, amount of substance, and absolute temperature of an ideal gas.

Real Gas: A gas that exhibits deviations from the ideal gas behavior due to the presence of intermolecular forces and the finite volume of the gas molecules.