Purpose of Residual property and Excess property in Thermodynamics

In summary, residual properties are used to calculate deviations from ideal gas states, while excess properties are used to modify models of substance behavior to account for deviations in real substances. They are both important tools in thermodynamics for accurately modeling natural phenomena.
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idiotblue
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Can anybody tell me what are Residual property and Excess property in thermodynamics for?
 
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Residual functions are used to calculate properties of substances at non ideal gas states. I have never heard of the Excess property myself. Perhaps someone else can answer that for you.

Hopefully this link works:
http://books.google.com/books?id=pRWqfsVTAY8C&pg=PA369&lpg=PA369&dq=residual+functions+thermodynamics&source=web&ots=h1kEfOVg4X&sig=u3SAlNM3dmMFYfFkANDhjB47igI [Broken]
 
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  • #3
Excess functions are introduced in Thermodynamics to modify simple models of substance behaviour (ideal gas model, ideal mixture model, ideal solution model), to account for deviations shown in real substances.

Source: http://imartinez.etsin.upm.es/bk3/c07/Excess functions.htm

This essentially means that it is a way to "adjust" your model so that it matches the natural phenomenon that you are modeling more closely.

It's like using a polytropic process with n=1.2 instead of 1.4 to allow for losses due to a gas having thermal losses/gains or doing some amount of work, etc.
 
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  • #4
Can anybody tell me what are Residual property and Excess property in thermodynamics for?

A Residual property is a a measure of the deviation from the value that some property would have for an ideal gas at the same conditions.

For example, if M is the actual value of a thermodynamic property (like the Gibbs free nergy) for a nonideal gas, and Mig is the value the property will have if the gas was ideal at the same T & P, then the residual property MR is defined as,

MR = M - Mig

Excess properties are usually used with liquid solutions, or when we want to measure deviations from a nonideal solution. The excess property is similarly defined as

ME = M - Mid

ie, the difference between the value of a thermodynamic property of the actual solution and an ideal solution at the same T,P and composition.

If you want a reference text, try Chapter 11 of "Chemical Engineering Thermodynamics" by Smith, Van Ness and Abbot.
 

1. What is the purpose of residual property in thermodynamics?

The purpose of residual property in thermodynamics is to account for the deviation of a substance's properties from those of an ideal gas. It takes into consideration the intermolecular forces and non-ideal behavior of a substance, which cannot be explained by ideal gas laws.

2. How is residual property related to excess property in thermodynamics?

Residual property and excess property are both used to describe the behavior of substances in non-ideal conditions. While residual property accounts for deviations from ideal gas behavior in a single phase, excess property describes the deviation from ideal behavior when two phases are present.

3. Why is it important to consider residual and excess property in thermodynamics?

Considering residual and excess property is important because it allows for a more accurate description of the behavior of substances in real-world conditions. Ideal gas laws do not account for the interactions between molecules, and therefore, cannot accurately describe the behavior of substances in non-ideal situations.

4. How are residual and excess property calculated?

Residual and excess property are typically calculated using equations that incorporate the deviation from ideal gas behavior. These equations may include parameters such as pressure, temperature, and molar volume.

5. How do residual and excess property affect thermodynamic processes?

Residual and excess property can affect the efficiency and accuracy of thermodynamic processes. In non-ideal conditions, these properties can cause deviations from expected behavior and may require additional calculations or adjustments in order to accurately describe the process.

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