What is Gas: Definition and 1000 Discussions

Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixture, such as air, contains a variety of pure gases. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer. The interaction of gas particles in the presence of electric and gravitational fields are considered negligible, as indicated by the constant velocity vectors in the image.
The gaseous state of matter occurs between the liquid and plasma states, the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention.
High-density atomic gases super-cooled to very low temperatures are classified by their statistical behavior as either Bose gases or Fermi gases. For a comprehensive listing of these exotic states of matter see list of states of matter.

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  1. greg_rack

    Speed of sound in an ideal gas

    First of all I thought it was necessary to calculate the temperature(the only data missing for the formula) using the ideal gas equation(since I've already been given 'p' and 'V'), and plug it in the 'v' formula, but the problem immediately occurred when i tried to find out the number of...
  2. J

    How Does the Ising Model Apply to Lattice Gas Systems?

    Hi everyone, even before addressing the following points I have a serious issue in understandig the text of the Exercise.My idea was to model this system with a lattice gas. Given that each site can host 2 atoms I have 3 possibilities for each site: I'll call'em ##S_{11} S_{00}## and ##...
  3. DaveC426913

    Gas filter mask on Mars - sci fi

    In the early parts of the books, Mars' ambient atmo pressure (and temperature) was increased, including not just CO2, but oxygen as well. It rose to the point where they only needed masks that let through oxygen but not CO2. In my amateur view, I would expect that this would not work very...
  4. A

    On the width of the kinetic energy distribution of a gas

    In these lecture notes about statistical mechanics, page ##10##, we can see the graph below. It represents the distribution (probability density function) of the kinetic energy ##E## (a random variable) of all the gas particles (i.e., ##E=\sum_{i}^{N} E_{i}##, where ##E_{i}## (also a random...
  5. Y

    Temperature change in a gas expansion

    1- ##\delta P_V =(\frac{\partial P}{\partial T} )_V \delta T_V## 2-##\delta V =(\frac{\partial V}{\partial T})_P \delta T+(\frac{\partial V}{\partial P})_T \delta P## so ##C_v \delta T=-P\delta V=-P((\frac{\partial V}{\partial T})_P \delta T+(\frac{\partial V}{\partial P})_T \delta P)## I can...
  6. Saptarshi Sarkar

    Why Does My Calculation of Maxwellian Gas Velocity Yield an Incorrect Result?

    I expanded it as shown above and got ##<v²> + <\bar v²> - 2<v><\bar v>## = ##v_{rms}^2 + \bar v^2 = \frac {3kT} m+\frac {8kT} {πm}## I used ##<v> = 0## as the velocity is equally likely to be positive as it's likely to be negetive. From the above I get the answer ##\frac {kT} m(3+\frac 8...
  7. tech99

    Is reducing energy losses critical for the success of hydrogen in the gas grid?

    A trial has commenced at Keele University in the UK where 20% Hydrogen is injected into the domestic gas supply. In this way it can be stored and then utilised by existing domestic burners. Can this be a quick solution to reducing domestic CO2 emissions? Or is it better to use battery storage...
  8. C

    Proof of second-order phase transition for a Van Der Waals Gas

    How is it proved that Van Der Waals gas is a second order phase transition? The second order derivative of the pressure (P ) with respect to volume ( V ) don't have a discontinuity ( except at point V = Nb , but the pressure is not existent for V<=Nb ). So how come Van der waals gas describes...
  9. N

    Suggestion for a gas discharge lamp

    There is a physics event being organized in my college for which I had planned to make a muon detector. I have the circuit ready which brings 240 volts ac mains source down to 80 volts dc supply. But now, I am facing a serious problem. I have been unable to find a neon glow lamp. Basically, mý...
  10. D

    Accounting for Liquid Water Density in Ideal Gas Pressure Calculations

    First calculate the total pressure, but that gives me p2=p1*t2/t1 = 2,86 bar and partial pressure of 0,87 bar which is wrong. any tips?
  11. B

    Mass of Gas Ejected: 1.25kg - Is it Reasonable?

    This is the problem below that I have tried doing I ended up getting the mass of gas ejected to be 1.25kg from doing the following Would you say this is a reasonable value to get Thanks in advance!
  12. CptXray

    Ideal gas in a cylindrical container

    It looks more like a computational obstacle, but here we go. Plugging all of these to the partition function: $$Q = \frac{1}{N! h^{3N}} \int -\exp(\frac{1}{2m}(p^2_{r}+p^2_{\phi}/r^2+p^2_{z})+gz)d\Gamma=$$ $$= \frac{1}{N! h^{3N}} \int \exp{(\frac{-1}{2m}p^2_{r})}dp_{r_{1}}...dp_{r_{N}}...
  13. Haynes Kwon

    I Determining Degenerate Gas in Stellar Structure

    When modeling stellar structure and formulating equation of states, I've seen various cases where you have to take into account whether the constituent gas of a star is degenerate or not. But how do you determine if the gas is degenerate or not?
  14. M

    A Irradition to base of cylindric gray gas volume

    Anyone who has an idea for how to calculate the irradition [W/m2] to the base of a cylinder with radius R, height H, absorption coefficient k, and temperature T? I've looked at the approach with mean beam length by Hottel but cannot figure out what to do when it is the base of the cylinder that...
  15. Aletag

    Work done BY the gas in a cyclic thermodynamic process

    Since the assignment asks the work done by the gas, that should be equal to P1*(V2-V1) aka the area under the P1 line. Do I have to subtract the work done to the system or is this the solution already? If so, why do I need P2?
  16. maxelcat

    Pressure of an ideal gas -- A Level Multiple Choice Problem

  17. A

    High pressure gas discharge fusion

    I thought to myself , have there any been any physical attempts or calculations in theory about the possibility of creating a net electrical gain of energy from a pulsed fusion approach where a high pressure/density gas mixture is prepared constantly within a container and a high current pulse...
  18. C

    B Irreversible expansion of gas against gas

    Let's say I have a liter of gas at pressure of 4 atm and T=900K. I use it to move perfect massless frictionless and insulative piston to compress a liter of 1 atm, T=300K gas. When the pressure on both sides is equal and the piston stops moving, will the temperature on both sides of the piston...
  19. berkeman

    Reflective inserts for home gas fireplaces

    I guess this applies to wood-burning fireplaces as well, but they will require more frequent reflector surface cleaning. Our gas fireplace is fairly warm, but it's clear that it's not as efficient as it could be. It seems like reflective back and side inserts would reflect a lot more of the IR...
  20. kevinmorais

    Carbon Dating Gases: Is It Possible and What Can We Learn?

    Can we Carbon Date a Gas or must it always be a solid?
  21. olgerm

    How to calculate entropy from positions and velocities of gas molcules

    How to calculate entropy from positions and velocities of gas molecules? lets say we have 2 different gases. entropy should be bigger after mixing them, than before when these are separated. But how to calculate exact entropies by knowing only positions and velocities of gas molecules?
  22. dRic2

    I Spin density in an (ideal) Fermi gas

    Hi, some time ago our professor told us (en passant) to evaluate this quantity: $$<F|n_m( \mathbf x) n_{m'}(\mathbf x) |F> - <F|n_m( \mathbf x)|F><F|n_{m'}(\mathbf x) |F>$$ And then he said: "you'll find that this quantity may not be zero. In particular when the electron are correlated it will...
  23. P

    A Half filling? Free electron gas? 2D tight binding lattice?

    It is well known that the 2D free electron gas fermi momentum can be expressed as follows, k_F=\left(2\pi n\right)^{1/2} where n is the electron surface density. Assuming this 2D electron system can be considered as 2-D tight-binding square lattice whose eigenergy can be written as...
  24. Frigus

    Why don't we consider ordered motion as part of the internal energy of a gas?

    Why we do not considered the translational energy of the gases particles in the internal energy due to ordered motion but only due to random motion.
  25. Moara

    Spherical gas distributed symmetricaly over space

    . We have that energy in a infinitesimal Spherical layer with number of mols dn is: dU=Cv.T.dn (1) But by the ideal gas law: PV=nRT (2) Differentiation gives: PdV+VdP=RTdn (3) (3) in (1) and using CV=3R/2 (monoatomic) gives: dU=3/2.(PdV+VdP) (4) Integration of (4) over the whole gas will...
  26. Zifan Wang

    Ideal Gas Law: Question about a compressor exam question

    This is a question in my midterm. I calculated for the answer as c) 11.7 atm by the Ideal Gas Law. The professor states that "all the air is originally at 1 atm" in the prompt indicates an idea of "both 70 L of air and existing 6 L of air in the tank are at 1 atm", and he grades d) 12.7 atm as...
  27. Sabra_a

    Universal gas constant R= Cp-Cv

    In the first question should I remove the delta and put d or that doesn't make a difference and on the second question should I substitute the values of R, K, Cv and Cp or that's not required I'm not really sure how correct is my answer to the second question
  28. B

    Ideal gas: Temperture at 1 atm

    Summary: U=3/2*n*R*T Can some of you help me with this The total internal energy of an ideal gas is 3770 J. If there are 3 moles of the gas at 1 atm, what is the temperature of the gas? I use U=3/2*n*R*T but get the wrong answer, (101 K) but it should be 303 K [Moderator's note: Moved from...
  29. Sabra_a

    Mass fraction and volume of a gas in a cylinder

    I have attached the full answer in PDF file. I'm not sure about the answers. will really appreciate if they get checked
  30. Diracobama2181

    Heat Capacity of a Fermi Gas at Low Temperature

    I find that $$U=\int Z \epsilon D(\epsilon) e^{-\epsilon β}d\epsilon=\frac{gV}{(2\pi)^3}\int Z \frac{(\hbar)^2k^2}{2m}k^2 (4\pi)e^{-β\frac{(\hbar)^2k^2}{2m}}dk$$ where g=2s+1=2, $$Z=e^{βµ}$$ and $$D(\epsilon)=\frac{gV}{(2\pi)^3}k^2 4\pi$$ for the density of states From here, I can use $$c_v...
  31. Diracobama2181

    What is the chemical potential of a diatomic gas in equilibrium?

    It is my assumption that I need to find the chemical potential of the atoms $$\mu_A$$ and for the molecules $$\mu_{A_2}$$, then use $$\mu_{A_2}+\mu_{A}=0$$ to arrive at the given identity. For $$\mu_A$$, I found that $$\mu_A=k_BTln(n_A\lambda ^3)$$, where $$n_a=\frac{N_a}{V}$$ and $$\lambda$$...
  32. C

    A Please help me understand this HO energy in He4 gas

  33. naushaan

    I Calculating Speed and Acceleration of a Gas Blob Orbiting a Massive Black Hole

    A mega-maser-emitting blob of gas is in orbit around a massive black hole in the centre of a galaxy. The black hole has a mass of 106 solar masses, and the blob of gas is in a circular orbit one light year away. What is the speed and acceleration of the blob?
  34. Ignitia

    Chemistry Calculate the Enthropy Change of Isothermal Expansion of a Non-Ideal Gas

    Part (a) ΔS = ∫ (dq/T) because: dq = PdV = (nRT/V)dV Then: ΔS = ∫ (1/T)*(nRT/V)dV ΔS = nR ∫(1/V) dV ΔS =nR[ln(V2/V1)] Part (b) This is where I'm stuck. I know [P + a/(v/n)2][v/n - b] = RT can be solved for P and simplified to P = [RT/(v-b)]-[a/v2] since n=1mol But I don't know how to proceed...
  35. S

    Need Help with Free Body Diagram of Oil & Gas Packer Tool

    Has anyone created a thread on Free Body Diagram on assembly having many components ? For example a Casing having premium threads in both end and a set packer within it. What would be the FBD equations to determine various forces and reaction forces
  36. S

    Combined Gas Law: Find Volume V2

    P1= 13.6 V1= 1.1 T1= 22 P2 = 14.4 V2= x T2 = 32 my answer is 1.51L am i missing something?　
  37. M

    Chemistry Ideal Gas Problem | Get Help Now!

    Hello guys. I really try to understand the problem, can you please help.
  38. TonkaTon

    A gas stream (1) contains 18 mol% hexane and remainder nitrogen flows

    Summary: Hello, I need some help with this problem since my professor is bad at explaining (he reads a book and repeats everything), there's a problem online similar, but values and what is asked is different. A gas stream (1) contains 18 mol% (40.2 mass%) hexane and remainder nitrogen flows...
  39. vishvajeet kadian

    Relation between temprature and pressure of a gas bieng compressed

    1. If a gas is kept at constant pressure of 1 atm & the temp. is raised upto the saturation temprature ( 99.97 C ) and just when Tsat is attained the heat transfer is stopped ( Hin & Hout both are 0 , adiabatic conditions ) . Now # If the adiabatic condition is maintained , then on...
  40. Nikhil Rajagopalan

    Heat Absorbed by Gas: An Expert Explanation

    Dear Experts, While going through the explanation why heat absorbed by a gas is path dependent, there were two examples of comparison. 1. A gaseous volume of 2 liters expanding slowly to 4 liters , supplying heat from a heater keeping the temperature of the gas constant at 300K. 2. A gas allowed...
  41. men5j2s

    Temperature of a compressed gas

    How can I calculate the temperature changes of a pressurized gas as it is in a cylinder, then as it is when flowing into another vessel? my best guess was using the ideal gas law (with help from this forum), but I feel like I'm using it wrong. P = 300bar or 296.08 atm V = 112 L (is this...
  42. men5j2s

    Can I calculate the flow rate of a compressed gas from pressure?

    I am using a compressed gas tank to fill an otherwise empty container, The gas tank is around 50bar and the container will be filled to 6bar. If I am using a pressure transducer to determine when the container has been filled to 6bar, can I use the information I gain from it to derive the flow...
  43. 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?
  44. T

    Diffusion of gas from a pond

    Trying to determine diffusion rate of a gas emitted from a body of water. I believe Fick's first law may apply: J = -D * (dc/dx) where: J = diffusion rate [mg/s×cm2] D = diffusivity constant (can be looked up based on type of gas and local air temperature) dc = change in concentration from...
  45. F

    Why does a helicopter float motionless but still consume gas?

    When a helicopter float motionless the work done on it is zero.But why does it still consume energy?A similar question is why when we hold still a weight, we must consume energy(we feel fatigue)?
  46. N

    Ideal Gas Law in Two Dimensions

    I am creating a two-dimensional model of an ideal gas, and I was wondering how I should determine initial velocity. Ideally, I would like for the simulation to reach a point where the velocity distribution resembles that of the maxwell-boltzmann curve — will this be achieved if I, say, assign...
  47. I

    Calculate Gas Behavior Step-by-Step in Simple Model

    Hi, I wish to write a simple simulation of gas behavior. I have two tanks, connected by a valve. When the valve is opened, the gas will obviously flow and after some time it will reach an equilibrium. I could really do with some help in calculating the rates of change of the temperatures and...
  48. H

    Partial Temperature of a Gas in a Mixture

    Is there such a thing as a partial temperature of a gas in a mixture? Partial pressure is commonly accounted for and used. It seems that if there are molecules of different masses colliding in a mixture, their average respective velocities in a mixture should be different based on transfer of...
  49. T

    B The Mysterious Shape of Jupiter: Why Gas Planets Stay Spherical

    If Jupiter is made of gas, how can it maintain its spherical shape without being contained in a spherical shaped container?
  50. schang04

    Calculate the time it takes for gas to fill a chamber (high P -> low P)

    How do you calculate the time it take a high pressured gas to fill a chamber? I have a gas in a chamber that is at 600psi and then another chamber at atmospheric pressure. When the valve between the two chambers is opened, how do you calculate the time it would take to fill the chamber? Are...
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