Thermal coefficient of expansion in gases

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Discussion Overview

The discussion revolves around the thermal coefficient of expansion in gases, specifically the value of γ and its derivation from the ideal gas law. Participants explore concepts related to gas behavior under temperature changes, including theoretical and experimental perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant states that the variation in a gas' volume is given by ΔV = γ⋅V[initial]⋅ΔΘ, questioning the value of γ=1/237.
  • Another participant requests a source for the γ value, indicating unfamiliarity with this specific coefficient.
  • A participant suggests that the correct value of γ should be 273 instead of 237, prompting a discussion about the ideal gas law and its implications.
  • One participant admits to not having learned about derivatives yet, indicating a gap in understanding the mathematical basis for the discussion.
  • Another participant provides an explanation of the experimental determination of the 273 value, referencing a specific section of a document that discusses the relationship between volume and temperature at constant pressure.
  • There is a mention of the concept of a perfect gas, with a participant expressing uncertainty about its definition and relevance to the discussion.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the value of γ, with some suggesting it should be 273 instead of 237. There is no consensus on the correct value or its derivation, and the discussion remains unresolved.

Contextual Notes

Limitations include varying levels of understanding among participants regarding derivatives and the ideal gas law, as well as differing interpretations of the thermal coefficient of expansion.

Who May Find This Useful

This discussion may be useful for students beginning to learn about gas laws, thermal expansion, and the mathematical relationships involved in these concepts.

Vittorio
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I know that the variation in a gas' volume is equal to ΔV = γ⋅V[initial]⋅ΔΘ with ΔΘ the variation in temperature and γ=1/237 the thermal coefficient of expansion in gases. Could someone please explain to me why γ=1/237 please ?
Thanks a lot,
V
 
Science news on Phys.org
Never seen this before. Do you have a source?
 
Vittorio said:
I know that the variation in a gas' volume is equal to ΔV = γ⋅V[initial]⋅ΔΘ with ΔΘ the variation in temperature and γ=1/237 the thermal coefficient of expansion in gases. Could someone please explain to me why γ=1/237 please ?
Thanks a lot,
V
From the ideal gas law, what is the derivative of volume with respect to temperature at constant pressure? (Are you sure about that 237, or should it be 273?)
 
Yes, sorry, I meant 273. My phycs teacher told me this, but I hadn't quite understood. Thanks a lot.
 
Vittorio said:
Yes, sorry, I meant 273. My phycs teacher told me this, but I hadn't quite understood. Thanks a lot.
What about my other question?
 
I haven't learned about derivatives yet.
 
Vittorio said:
I haven't learned about derivatives yet.
Are you familiar with the ideal gas law?
 
I think - a perfect gas is a gas in which there are no chemical reactions between the molecules. I'm not sure, I'm just starting to learn about gases and expansion etc.
 
For your background it may be more useful to read about the experimental side of the thermal expansion. The 273 value can be determined by extrapolating experiments on gases, as described in section 17.4 of the link below:

http://www.farmingdale.edu/faculty/peter-nolan/pdf/UPCh17.pdf

If you plot the volume versus temperature at constant pressure, you get a straight line which will correspond to zero volume for a temperature of about -273 Celsisus.
The nice thing is that this extrapolated temperature is about the same for all gases (exactly the same for ideal gases, of course). So this led to the definition of an "absolute" temperature scale.
 
  • #10
Vittorio said:
I think - a perfect gas is a gas in which there are no chemical reactions between the molecules. I'm not sure, I'm just starting to learn about gases and expansion etc.
Google "Ideal Gas Law"
 

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