First order phase transition (van der waals gas)

In summary, the conversation discusses the physical explanation of two graphs on page 4 of a document. The graphs show that Vg decreases with temperature while Vl increases with temperature. The Maxwell construction is referenced, which explains that as temperature rises, the two loops in the theoretical p-V curve become less pronounced until they disappear at the critical point. This causes Vg and Vl to coalesce and decrease in distance with temperature.
  • #1
jasony
11
0
I am looking at some of the notes but don't quite understand this.

What are the physical explanation of the graphs (Fig 4(a) and 4(b)) on Page 4 ?
http://www.pma.caltech.edu/~mcc/Ph127/b/Lecture3.pdf"

Why [tex]V_{g}[/tex] decreases with temperature but [tex]V_{l}[/tex] increases with temperature?
 
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  • #2
Anyone who can help? please...
 
  • #3
Look at the Maxwell construction: When the temperature rises, the two loops in the theoretical p-V curve become less and less pronounced until they disappear at the critical point. At the critical point Vg and Vl coalesce, hence the distance of Vg and Vl has to decrease with temperature.
 

1. What is a first order phase transition?

A first order phase transition is a type of phase transition that occurs when a substance changes from one state to another, such as from a solid to a liquid or from a liquid to a gas. This type of transition is characterized by a sudden change in the properties of the substance, such as its density, temperature, or pressure.

2. What is a van der Waals gas?

A van der Waals gas is a theoretical model of a gas that takes into account the attractive and repulsive forces between molecules. It is named after Dutch scientist Johannes Diderik van der Waals, who introduced the concept of intermolecular forces in the late 19th century. This model helps to explain the behavior of real gases at high pressures and low temperatures.

3. How does a van der Waals gas differ from an ideal gas?

An ideal gas is a theoretical model that assumes that gas particles have no volume and do not interact with each other. On the other hand, a van der Waals gas takes into account the size and interactions of gas particles, resulting in a more accurate representation of real gases at high pressures and low temperatures.

4. What is the critical point of a first order phase transition?

The critical point of a first order phase transition is the specific combination of temperature and pressure at which the two phases of a substance coexist in equilibrium. At this point, the substance has the same density and other physical properties in both phases, and any further increase in pressure or temperature will result in a complete transition to one phase.

5. How is the van der Waals equation used to describe a first order phase transition?

The van der Waals equation is an improvement on the ideal gas law that takes into account the volume and intermolecular forces of gas particles. By including these factors, the equation is able to accurately describe the behavior of gases at high pressures and low temperatures, including first order phase transitions. It allows for the calculation of the critical point and the determination of the coexisting phases at different combinations of temperature and pressure.

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