Talk:Ideal gas

message: The entropy change for an ADIABATIC process between two well defined equilibrium states IS ZERO!! (the one written there is valid just because Cp-Cv=R for an ideal gas, but zero is what should appear in the table!).
If the process is irreversible and adiabatic, all we can say is that entropy increases (whatever the system) - and the same two states connected through the reversible adiabat (isoentropic) cannot be connected through an irreversible, adiabatic process.  —Preceding unsigned comment added by 18.82.6.138 (talk) 19:13, 25 September 2008 (UTC)
thread_title:  comment 

message: The b term is an excluded volume term. It's there because gas molecules have a certain size, and two cannot coexist at the same place. Van Der Waals gas is very important because its theory is also the base for the description of liquid mixesUser:ThorinMuglindir
(81.57.151.89) 11:53, 23 October 2005 (UTC)
thread_title:  old comment 

message: "Generally, deviation from an ideal gas tends to decrease with lower temperature and higher density (i.e., higher pressure)[...] The ideal gas model tends to fail at lower temperatures or higher pressures[..]"
Maybe i am misunderstanding but if the deviation from the model decreases with temperature then it shouldn't mean that it will fail, actually the opposite.Ptsneves (talk) 18:24, 8 November 2010 (UTC)
thread_title: Contradiction

message: Perfect Gas vs. Ideal Gas
Perfect Gas should NOT redirect to this page and the first statement in this article is incorrect. Perfect gases and Ideal gases are NOT the same thing!  Katanada (talk) 21:19, 11 January 2008 (UTC)
replies: text: Umm, so why not build a Perfect Gas page (preferably with references - unlike this one:-) and correct and link the ideal gas page to it?  (The current Ideal Gas entry is reference free and looks like much of it was lifted from a textbook.) ComputerGeezer (talk) 15:47, 31 January 2008 (UTC)
replies: text:  see, I would do that kind of thing but the amount of changes that need to be made are on the @ikiproject type scale. This whole article needs to be redone and split into various articles for the different topics. Basically, I can't do this on my own and honestly, I don't have enough time to re-write everything. I may have more time once I'm done with this semester but in the meantime I'll just leave stuff on the talk page and hope more people respond and want to help me re-write this article and write new ones.Katanada (talk) 09:47, 2 February 2008 (UTC)
replies: text:  So I joined the physics and chemistry Wikiprojects and I'm currently working on the gas page. I'll get back to this ideal gas page as soon as I finish that one! Katanada (talk) 07:40, 25 February 2008 (UTC)
replies: text: Why not improve the article stepwise instead of disputing correctness? Bo Jacoby (talk) 15:50, 25 February 2008 (UTC)
replies: text: Thats exactly what I'm doing this week! I'm finally on Spring Break. Please check out Gas to see the types of changes that I'm making. Katanada (talk) 16:23, 25 February 2008 (UTC)

text:  I just finished gas. I'll try to get a start on this article soon.Katanada (talk) 04:22, 26 February 2008 (UTC)
thread_title:  Disputed 

message: A perfect gas is one with specific heats that are independent of the temperature T.
The “perfect gas approximation” has nothing directly to do with whether a gas is ideal or not (though because non-ideal gas behavior can appear at very low temperatures, cp may be considerably different at those temperatures than at, say, 300K).
As long as the number of DOF’s of the molecules does not change with temperature T, then the specific heats Cv and Cp will be constant and thus the gas will be “perfect”. A perfect gas is simply one that has constant specific heats.
Katanada (talk) 21:10, 11 January 2008 (UTC)
thread_title:  Perfect Gas 

message: An ideal gas is one in which the separation between molecules is sufficiently large (i.e.,
the density is sufficiently low) that intermolecular (van der Waals) forces are negligible,
so that the gas satisfies the ideal gas law. A gas ceases to be “ideal” when the density becomes very large (e.g., at very high pressures and/or low temperatures), so that the intermolecular forces become large enough to produce substantial departures from the ideal gas law. The gas then instead follows non-ideal behavior of the form PV = ZRT where Z is a “Compressibility factor”
Katanada (talk) 21:10, 11 January 2008 (UTC)
replies: text: Looks like you need a reference here.  Page 8 of Atkins' 8th Edition "Physical Chemistry, which is the canonical physical chemistry textbook around these parts, states in no unclear terms: perfect gas and ideal gas are synonyms.  —Preceding unsigned comment added by 146.6.143.48 (talk) 03:36, 20 February 2008 (UTC)
replies: text:  Then the Atkins' 8th Edition "Physical Chemistry" is incorrect. There are 3 general models of gases: the "Real Gas" model is based on the generalized compressibility chart which introduces a 'fudge factor' (Z) into the IGL [PV=ZRT]. An "Ideal Gas" is just the specific case of the "Real Gas" model where Z=1. The "Perfect Gas" model is a specific case of an "Ideal Gas", they both obey [PV=RT]; however, the specific heats are assumed constants. Look it up on Google! :-) I have references from 3rd Edition Modern Compressible Flow, 2nd Edition Mechanics and Thermodynamics of Propulsion, and 4th Edition Fundamentals of Aerodynamics, and the NASA website.Katanada (talk) 05:51, 20 February 2008 (UTC)
thread_title:  Ideal Gas 

message: Well done, PAR. Just a few suggestions.
* We have once told that kN=nR, so don't repeat it
: - done
* Use the dimensionless entropy S/kN
: - I can't find a natural point for introducing this which doesn't clutter things except the final equation, when it is clear that everything is intensive, so thats the only one I changed.
* Don't restrict the analysis to monatomic gases, but use the symbol rather than the constant value 3/2 for the dimensionless heat capacity at constant volume.
: - done
* An intermediate result would be helpful after the integral
: - That integration was messed up - I fixed it, hopefully its clear now.
* The value of the Sackur-Tetrode equation is unclear: "The simple formula breaks down at low temp. So introduce the S-T equation. That breaks down too". So what is the point ? Bo Jacoby 12:47, 9 November 2005 (UTC)
replies: text: - Tried to make that a little clearer. PAR 16:46, 9 November 2005 (UTC)
thread_title: The entropy of an ideal gas

message: Found this statement :Gases are most ideal at high temperatures and low densities.
This is WRONG since gases at higher temperatures will have MORE collisions hence the "ideal gas" property is lost (as you may be aware molecules have inelastic collisions hence kinetic energy is lost). Also at lower temperatures the distance between particles is greater, hence there is more interaction between molecules. Therefore, a gas which is at extremely high/low temperatures (in comparison to standard labratory conditions) will not obey the ideal gas laws fully. 
The low density may also be checked. 
I have removed this nonsense. Thanks  —Preceding unsigned comment added by 121.222.226.157 (talk) 08:54, 23 October 2007 (UTC)
replies: text: Actually, the statement that gases are most ideal at high temperatures and low densities is generally true.  The point you make about more collisions at higher temperatures resulting in more lost kinetic energy is a second order effect since most molecular collisions are elastic.  The first order effect of higher temperatures is that the internal energy of the gas is high enough to make negligible the long-range interactions between molecules.  This is another point of confusion on your part -- the difference between collisions and interactions.  "Interactions" refers to long-range forces that act between molecules, eg. van der Waals.  In other words, the molecules move in a potential field due to the presence of other molecules.  At high temperatures however, the kinetic energy term dominates and the potential term becomes negligible.  At low densities, the average distance between molecules becomes greater, again reducing the interactions between molecules.  Under both of these conditions, gases will tend to have internal energies that are strictly kinetic, ie. U = CvNkT.  In other words, they become ideal... Peebeewee (talk) 22:20, 11 February 2008 (UTC)
replies: text: It also depends on the gas itself and molecule dissociation which then deals with high temperatures (the dissociation point has a dependence on pressure as well). Somehow I feel there should be some talk about the compressibility factor in here to more clearly describe the "non-ideal-ness" of high-temperature, high-pressure gases. Katanada (talk) 01:51, 14 February 2008 (UTC)
replies: text: I have added experimental values, at the Compressibility factor page - this should provide solid ground to solve this little dispute. Power.corrupts (talk) 13:05, 30 September 2008 (UTC)
thread_title:  Totally wrong 

message: Isn't it wise to specify that p is the absolute pressure? Not only here, but virtually anywhere pressure is mentioned. Even if it were clarified somewhere else, which I don't know, this lack of information is unpractical to the average user. 
I'm asking because I'm new to WP and I don't want to mess around with articles! Podi74 (talk) 12:19, 19 December 2007 (UTC)
replies: text: Yes, it would be useful to at least mention that the pressures in this article are absolute pressures, and not "gauge pressures". For atmospheric measurements near sea level on the planet Earth, in the English sustem of units, the conversition equation is approximately: Absolute Pressure = Gauge Pressure + 14.7 pounds per square inch. You may surely write a slightly-different equation when dealing with the unit pascal, which is one newton per square meter.98.67.106.251 (talk) 19:37, 4 May 2009 (UTC)
thread_title:  Absolute vs relative pressure 

message: By introducing the undefined concept of 'moderate temperature' an editor has made the text nonsensical. Bo Jacoby (talk) 09:31, 20 February 2008 (UTC)
thread_title:  moderate temperature 

message: Perhaps RIPE would be a better acronym, rather than PRIE? PRIE is just a collection of letters, RIPE actually spells something, so it is easier to remember, especially for students. Just a thought.  —Preceding unsigned comment added by 151.200.36.227 (talk) 04:15, 2 May 2008 (UTC)
thread_title:  acronym 

message: "...the classical thermodynamic ideal gas is based on classical thermodynamics..."?  —Preceding unsigned comment added by Paranoidhuman (talk • contribs) 02:45, 12 August 2009 (UTC)
thread_title: thermodynamics or statistical mechanics?

message: This is nonsense:
:\hat{c}_V is a constant dependent on temperature (e.g. equal to 3/2 for a monatomic gas for moderate temperatures)
Constants do not depend on temperature. 3/2 does not depend on temperature. The meaning is that \hat{c}_V is constant for the simplified model of ideal gases but vary for real gases. So it should state that
:\hat{c}_V is the dimensionless specific heat capacity at constant volume, equal to 3/2 for monatomic gas, 5/2 for diatomic molecules and 6/2 for more complex molecules. 
Bo Jacoby (talk) 09:07, 12 September 2010 (UTC)
thread_title:  Perfect nonsense 

message: The last sentence in this section seems spurious or at least sits at the wrong place: "Ideal gasses are not found in the real world. So they are different from real gasses. There are basic assumptions made in the kinetic theory of gasses". 
Second: in this sentence gasses is written with double S. http://www.collinsdictionary.com/dictionary/english/gas says both forms are allowed, but the other occurrences on this page have a single S. --46.115.56.114 (talk) 00:07, 23 August 2012 (UTC)
replies: text: Agreed and deleted. Next time, you can delete such a sentence yourself, as long as you explain your reason in the edit summary or on the talk page. Han-Kwang (t) 11:28, 25 August 2012 (UTC)
thread_title:  Multicomponent systems 

message: Spherical particles are not necessary, only that the interparticle distance be large. What is needed that rotational energy is negligible. Spherical particles will have a rotational energy. If they are small enough, it will be negligible. I will change this soon. PAR (talk) 16:24, 14 September 2012 (UTC)
thread_title:  Ideal Gas Assumptions 

message: Classical thermodynamic ideal gas description contradicts the definition of an ideal gas.
The definition states "composed of a set of non-interacting point particles".
Classical thermodynamic ideal gas description talks about spherical particles that collide. This sounds wrong and should be removed or explained properly.  — Preceding unsigned comment added by 2401:FA00:0:3:BE30:5BFF:FEE1:EBF4 (talk) 04:53, 30 October 2013 (UTC)
replies: text: There is no need to include the requirement of "non-interacting" particles to obtain an ideal gas.  That is overly restrictive.  A better definition of an ideal gas would be that it is any gas which obeys the ideal gas law.  Going beyond that, to pick a specific model which obeys the ideal gas law and saying that is the only ideal gas, is too much.  The "definition" of an ideal gas in the first paragraph needs more careful thought. 3piecesuits (talk) 07:30, 29 December 2013 (UTC)
replies: text: If that's the case, it would be nice to include an example of a gas with interacting particles that is nevertheless ideal. Do you know of one? PAR (talk) 15:03, 30 December 2013 (UTC)
thread_title:  Contradiction 

message: I'm still trying to understand the heat capacity section.  If you compare to the article on Heat capacity, there's no point where the variables with bars over them are introduced.  I can't see such an introduction in this article.
Now, there is a meaningful difference between the heat capacity and the specific heat capacity.  But this is generally designated with upper case versus lower case.  It's not clear at all what the bars above the variables mean.  I think some description should be added.  But I don't know what it means, so could anyone help me? -Theanphibian (talk • contribs) 19:39, 21 March 2014 (UTC)
thread_title:  Barred variables - what does this mean? 

message: I have a very nice ideal gas simulation (in Java) available here: http://www.ics.uci.edu/~wayne/Gas . Does anybody I'm totally new to editing Wikipedia articles and don't know if it would have a place or if so where to put it.  If anybody thinks there is a place for such a simulation please contact me at whayes@uci.edu (Wayne Hayes, UC Irvine) Waynehayes (talk) 14:40, 15 April 2014 (UTC)
replies: text: Here is a simulation.Chjoaygame (talk) 22:00, 15 April 2014 (UTC)
thread_title:  Place for an interactive ideal gas simulation? 

message: I have undone a faulty good-faith edit that has an edit summary "corrected standard molar volume. It is 22.4 at 101.325 kPa".
The relevant sentence, as I have restored it, reads
:::::One mole of an ideal gas has a volume of 22.7 L at STP as defined by IUPAC.
The relevant text at the linked page reads
:::::In chemistry, IUPAC has established two standards:
:::::* standard temperature and pressure (STP) as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 100 000 Pa (1 bar, 14.5 psi, 0.98692 atm).
By my arithmetic, .
It is more or less routine that this correction appears here.Chjoaygame (talk) 05:42, 14 December 2015 (UTC)
thread_title:  undid faulty good-faith edit 

message: The expression for computing the  entropy of ideal gases given in the text as
:\Delta S = \int_{S_0}^{S}dS
=\int_{T_0}^{T} \left(\frac{\partial S}{\partial T}\right)_V\!dT
+\int_{V_0}^{V} \left(\frac{\partial S}{\partial V}\right)_T\!dV
is a little problematic. The entropy is a function of temperature and two extensive variables  V,N : 
: S = S(T,V,N) 
therefore, tho compute the change in the entropy during a transformation, we must write  
:\Delta S 
=\int_{T_0}^{T} \left(\frac{\partial S}{\partial T}\right)_{V,N}\!dT
+\int_{V_0}^{V} \left(\frac{\partial S}{\partial V}\right)_{T,N}\!dV
+\int_{N_0}^{N} \left(\frac{\partial S}{\partial N}\right)_{V,T}\!dN
Somehow, the third term (the variation in  S  due to variation in  N ) has been omitted, but the correct expression for  S  is obtained when  N  is varied in the section on chemical potential. This need some clarification/cleaning.  — Preceding unsigned comment added by BahramH (talk • contribs) 05:43, 22 August 2016 (UTC)
thread_title:  Entropy of ideal gas (again) 

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thread_title:  External links modified 

message: "The molecules of the gas are indistinguishable, small, hard spheres"
vs.
"the Equipartition Theorem predicts that the constant for a monatomic gas is $\hat c_v = \frac 32$ while for a diatomic gas it is $\hat c_v = \frac 52$ if vibrations are neglected"
So do gases that are non-monoatomic count as ideal or not? The ideal gas law sure applies to them. I would consider them ideal gases as well. In consequence, the microscopic model of an ideal gas should not speak of "hard spheres" is insufficient. Maybe it is more inclusive to speak of "hard collisions" between molecules of whatever shape. Although, what about vibrational degrees of freedom?  — Preceding unsigned comment added by Benzh (talk • contribs) 14:55, 12 December 2019 (UTC)
thread_title:  Are diatomic gases ideal? 

message: An editor has asked for a discussion to address the redirect Behaviour of gases. Please participate in the redirect discussion if you wish to do so.  Utopes (talk / cont) 19:00, 31 March 2020 (UTC)
thread_title:  "Behaviour of gases" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]] 

message: why is there a non-peer-reviewed working paper randomly inserted in this Wikipedia page?  Seems wildly inappropriate. 108.48.50.164 (talk) 20:56, 11 July 2023 (UTC)
replies: text: Seems to have been some form of WP:REFSPAM.  Headbomb {t · c · p · b} 21:05, 11 July 2023 (UTC)
thread_title:  Random chemrxiv citation