What is Real gas: Definition and 45 Discussions

Real gases are nonideal gases whose molecules occupy space and have interactions; consequently, they do not adhere to the ideal gas law.
To understand the behaviour of real gases, the following must be taken into account:

compressibility effects;
variable specific heat capacity;
van der Waals forces;
non-equilibrium thermodynamic effects;
issues with molecular dissociation and elementary reactions with variable compositionFor most applications, such a detailed analysis is unnecessary, and the ideal gas approximation can be used with reasonable accuracy. On the other hand, real-gas models have to be used near the condensation point of gases, near critical points, at very high pressures, to explain the Joule–Thomson effect and in other less usual cases. The deviation from ideality can be described by the compressibility factor Z.

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  1. G

    I Heat capacity for a real gas using the ideal gas (zero pressure) equation

    Summary:: Heat capacity for real gas with ideal gas (zero pressure) equation I'm looking at this problem and I'm stuck. I usually question everything but this problem is confusing me. I don't know how they've made the jump from reduced properties (from generalized Cp charts(?)) to...
  2. MichPod

    I Why the statistics for a real gas are not quantum in nature?

    A gas of bosons or fermion particles follows a particular quantum statistics. Then why a molecular gas (say, H2) follows a classical distribution statistics? Is it not the case that the molecules should be indistinguishable one from another and be either bosons or fermions? What is exactly the...
  3. Kaushik

    Van der Waals constant 'b' for a real gas

    Doesn't volume of ideal gas include volume of the molecules? What I was taught in school is that, when two molecules collide, no other molecule can come around it (inside the green part in the figure) and that volume is excluded volume? Is it correct? If yes, why?
  4. W

    Equation of state for a real gas

    My work was as follows: The first law states ##dU = TdS - PdV##, and thus $$p =- (\partial U/\partial V)| _S$$ $$U = -RT \ln(V-b) + f(S)$$ To determine ##f(S)##, I reasoned that in the ideal gas limit of ##b = 0##, ##U## should take the form of the ideal gas' molar internal energy ##\frac{3}{2}...
  5. P

    A Free expansion of a real gas vs Joule-Thomson effect

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  6. L

    Final temperature real gas behaving ideally

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  7. ScottAllenRauch

    Fluid Flow Loss Analysis Using Real Gas Properties

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  8. M

    I Is it Reasonable to Assume (3/2)*P*V as the Internal Energy of a Real Gas?

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  9. arpon

    Adiabatic process of real gas

    Homework Statement Show that for a gas obeying the van der Waals equation ##\left(P+\frac{a}{v^2}\right)(v-b)=RT##, with ##c_v## a function of ##T## only, an equation for an adiabatic process is $$T(v-b)^{R/c_v}=constant$$ Homework Equations ##TdS=c_vdT+T\left(\frac{\partial P}{\partial...
  10. K

    Real Gas Problem Homework Help

    Homework Statement The task is the following: Homework EquationsThe Attempt at a Solution I calculated the derivatives for Vm (crit) and set them = 0, but somehow I can't solve the equation to obtain Vm (crit) on one side alone. This is how far i managed to do it: Can someone help me?
  11. S

    How was the van der Waals equation derived?

    the equation (P+a(n/V)^2)(V-nb)=nRT was derived in this manner: The pressure of a real gas is affected by intermolecular forces and so the a(n/V)^2 term must be added to the measured pressure to obtain the ideal pressure where Pmeasured+a(n/V)^2=Pideal On the other hand when they explained...
  12. VoteSaxon

    Van der Waals and boiling point

    Homework Statement The bulb of a constant volume gas thermometer is immersed in an ice/water/water vapour mixture at equilibrium and the recorded pressure is 0.400 atm. It is then immersed in a boiling liquid and the pressure is 0.844 atm. Sufficient gas is then removed from the bulb such that...
  13. S

    Compressibility factor and van der Waals equation for temp

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  14. S

    Question about compressibility factor

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  15. HelloCthulhu

    Electrolysis System Work and Real Gas Law

    Greetings Everyone! I read a very good thread regarding how Ideal Gas Law is used to calculate system work for the electrolysis of water: W = PΔV = (101.3 x 103 Pa)(1.5 moles)(-22.4 x 10-3 m3/mol)(298K/273K) = -3715 J https://www.physicsforums.com/threads/work-of-electrolysis-of-water.756240/...
  16. B

    Adiabatic expansion of a real gas

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  17. Soho

    Temperature varying in vacuum chamber during pressure adjust

    Hello everybody, I am working on some tests on materials and structures in a vacuum chamber. I noted that during the final moments of the pressure rising (when I open the valve to let the air in), temperature sensors installed in the chamber record the temperature rising more than ten degrees...
  18. MexChemE

    Enthelpy change for a real gas (Carbon dioxide)

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  19. H

    Real gas equation in terms of Cv?

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  20. fluidistic

    Real gas, unable to reach the correct expression

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  21. B

    Calculating Temperature Change in Real Gas Isolated Chamber with Changed Volume

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  22. T

    How Does Potential Energy Affect the Internal Energy of Real Gases?

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  23. J

    Isentropic Relations for Real Gas in Converging-Diverging nozzle

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  24. M

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  25. O

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  26. M

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  27. L

    Heat capaticy of isobaric process with real gas

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  28. H

    A real challenge: real gas isothermal delta h

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  29. A

    How can I find the adiabatic equation for real gases?

    Hey! Maybe anyone knows, how to get real gas adiabatic equation. It's not a big deal, when you need to get ideal gas equation, but I haven't got any ideas about real gas. I'm wondering maybe it's something with Van der Waals equation, but in my opinion it can't be like this ...
  30. C

    Is Entropy Change of a Real Gas Dependent on Path in Reversible Processes?

    For a real gas (non-ideal gas) in a reversible process, the way to calculate \Delta{S} should also be independent to path simply because entropy is a state function. However, I got strange solution while taking different path. Here is the condition: 1. Equation of state (EOS) for the real gas...
  31. C

    Alternative Real Gas Equation of State

    1. A friend suggests to you an alternative to the Virial equation of state: P=(RT/Vm)-(B/Vm2)+(C/Vm3) a.) Show that this equation is useful by proving that it demonstrates critical behavior. b.) Find the critical constants Pc, Vm,c, and Tcin terms of B, C and R. c.) Calculate the...
  32. A

    Real Gas PV Curve: Volume Explained

    http://faculty.wwu.edu/vawter/PhysicsNet/Topics/Thermal/gifs/vdWaalEOS02.gif After the gas has been liquified, the gas volume should have disappeared. Why the liquid part of the curve still possesses volume?
  33. R

    Real gas compressibility isotherms(graphs)

    Homework Statement Sketch the following compressibility isotherms(fancy word for graphs) (compressibility factor, PV/nRT versus pressure :) for oxygen at a temperature just above the critical temperature ::) for oxygen at a temperature well above the critical temperature eg. 200 degrees...
  34. C

    Adiabatic Expansion of a real gas

    I am having trouble with the very last part of this question. I will write the whole question just to make sure that I haven't screwed up the first part too :) When a certain freon used in refrigeration was expanded adiabatically from an initial pressure of 32 atm and 0degrees C to a final...
  35. kandelabr

    Real gas tables: isentropic work

    Hello. I am writing a Matlab program for calculating properties and processes of dry air using real gas tables. The only tables I could find were from Perry's Chemical Engineer's Handbook (7th edition, 1999). Mostly I make use of cubic interpolation and in some critical cases numerical...
  36. kandelabr

    What are the equations of state for air at high pressures and temperatures?

    Hello, I am looking for a real gas equation of state for air, if possible a MATLAB script. I am working on pressures up to 500 bar and to 500°C. The thing is that I not only need a p-v-T relation, I also need to calculate work done by compressed air and heat that is involved in...
  37. L

    Calculate the number of moles in a real gas

    Homework Statement I would like to know how to calculate how much moles of gas I have in the following in a cylinder with a certain volume and pressure. The gas in the cylinder is a mixture of air, with added oxygen and helium, the mixture is 18% Oxygen, 36,6% Nitrogen, 45% Helium and 0,4%...
  38. 1

    Real Gas vs Ideal Gas: Compressibility Ratio

    The compressibility ratio of a gas is PV/nRT. What happen to the compressibility ratio if the attration force between the gas molecules increase? The answer says it decreases because the more molecules interact with each other, so the pressure they exert on the container decreases, thus...
  39. kandelabr

    Does Throttling Compressed Air Cause Liquefaction?

    Homework Statement I need to know what happens if compressed air from a vessel at room temperature is throttled from 450 bar to 2 bar. Homework Equations I know Joule-Thomson effect (http://http://en.wikipedia.org/wiki/Joule-Thomson_effect" ) deals with this, but I'd need it explained a...
  40. Y

    MC: Chemistry Ideal Gas vs Real Gas

    Homework Statement 24. At constant temperature, the behavior of a sample of a real gas more closely approximates that of an ideal gas as its volume is increased because the: a. Collisions with the walls of the container become less frequent b. Average molecular speed decreases c. Average...
  41. A

    Can Real Gases Have a Lower Pb/Pm Ratio Than Ideal Gases?

    Ok, let's say we have at our disposal a thermometer of constant volume gas. Inside it, we'll put a real gas, like Helium or Molecular Hydrogen. Ok, the gas compartment is placed inside a mixture of liquid water and ice, so we guarantee the gas inside is at 273.15 K. We measure its pressure...
  42. S

    Real vs Ideal Gas: Pressure & Temperature Effects

    If a sample of air had high pressure and high temperature, would it be a real or ideal gas?
  43. C

    Beattie-Bridgeman Real Gas Model

    I need to calculate the compressability of several gases as they are being added to a storage cylinder. I would like to use the Beattie-Bridgeman equation as described here. I need to be able to compute the Z factor (compressability) for a given gas at a given pressure. I am a bit new to...
  44. P

    Difference between an ideal gas and a real gas

    Hey Could somebody please explain what the difference between an ideal gas and a real gas are? Or post a suitable link from which I can understand the concept surrounding this issue. Thanks Pavadrin
  45. N

    Real Gas Laws: Exploring Alternatives to PV=nRT

    the ideal gas law PV=nRT only can used on the ideal gas, right? if the we want consider the real gas... what equation should we used??
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