Real Gases and Van der Waals Isotherms

Study Notes

Isotherms in Real Gases

Isotherms are graphical representations of the pressure (P) of a gas as a function of its volume (V) at a constant temperature (T).

Van der Waals Isotherms vs Ideal Gas Isotherms

Unlike the ideal gas isotherms, which are perfect hyperbolas described by Boyle's law (PV = constant), Van der Waals isotherms exhibit more complex behavior.
The Van der Waals isotherms deviate from the ideal gas law due to the inclusion of intermolecular forces and finite molecular volume.

Characteristic Feature: Van der Waals Loops

A distinctive characteristic of Van der Waals isotherms is the presence of "loops" at lower temperatures. These loops indicate that the gas can exist in multiple states (liquid, vapor, or a mixture) at a given pressure and temperature.
These loops are not physically realistic and represent an artifact of the Van der Waals equation.

Approximating Ideal Gas Laws

The Van der Waals isotherms approximate the ideal gas laws more closely at high temperatures and low pressures.
Under these conditions, the intermolecular forces and molecular volumes become less significant compared to the average kinetic energy of the gas molecules.

Van der Waals Equation Modification

The Van der Waals equation modifies the ideal gas law by introducing two correction terms:
- a/V^2: accounts for the attractive intermolecular forces between gas molecules.
- b: accounts for the finite volume occupied by the gas molecules.
The Van der Waals equation is: (P + a/V^2)(V - b) = RT

Description

This quiz delves into the properties of isotherms in real gases, focusing on the distinctions between Van der Waals isotherms and those of ideal gases. You'll explore the conditions under which real gas isotherms approximate ideal gas behavior and the modifications introduced by the Van der Waals equation. Perfect for students studying thermodynamics!