Gas Definition and 1000 Threads

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.

View More On Wikipedia.org
Recent contents Top users
  1. Calstiel

    Question About Ideal Gas and Average Free Movement of Molecules

    Hello, I have a question regarding the ideal gas and the average free movement of a single molecule. For simplicity, let's consider a model where we have only one atom moving, and we assume all atoms have the same radius. First, we calculate the cross-section σ using the formula σ=d², where d...
  2. L

    Confusion about work done by a gas - Thermodynamics

    This is chemistry but it's basically physics :D. I used PV = nRT, I get V = 37.44 L. This is fine. So then I have W = P(Vfinal - Vinitial). Vinitial is zero, because there was no hydrogen gas initially. So I get 3.78 kJ. And as the gas expanded from 0 L to 37.44 L, the gas has done positive...
  3. G

    B How the temperature of the Earth's surface affects the air pressure above it

    If the surface is heated, air above it will also heat, its temperature will rise. It will cause two processes: while temperature of gas rise, its pressure will also increase, but, also, as the air molecules get more energy, they will go higher from the earh surface, concentartion of the...
  4. U

    I Energy transfer during gas discharge

    It is known that while the electric current flows along the wire the energy propagates through the field near that wire (and not by means of electron gas kinetic energy) and the electrons' velocity is equal approximately to 10^[-3] m/s. Meanwhile, the electrons' velocity during the gas...
  5. highschoboy004

    Heated gas pushing a mercury column out of a cylinder

    Firstly I figure out that there is a point where the temperature of the gas is the hottest and beyond that no more amount of heat is necessary, descibed as following inequation:
  6. L

    I How to calculate the mass of gas in a tank?

    Dear community, I have a question comparable to https://www.physicsforums.com/threads/calculating-the-mass-of-air-in-a-pressurised-air-tank.1053707/, but with some additional peculiarities. My setup is: 1) I got a time series of gas pressure and temperature, with a time step of 2 minutes 2) I...
  7. Steven Bolgiano

    I Gas Pressures and the Resistance of Materials (Biodigester Generates Methane)

    Hi Physics Forum Folks! What an amazing resource of knowledge, ... thanks! The question is on the attached graphic, as its much more clear with an illustration. (Please read questions on this graphics first before looking at the video below,) This video is a very quick look at the actual...
  8. hraghav

    Calculating work done by a gas

    I have found the answers for T = 848.615K, P = 126137.7705 Pa and change in S = -184.27008 J/K. But my answer for work is not correct and I am not sure where I am making an error. Could someone please help me out with how to calculate work? My steps for work is : We are given: Pi = 101325 Pa Pf...
  9. K

    Help with Calculation: Thermal Expansion of Neon

    If neon is stored at 40 psi . 65 degrees fahrenheit. How do i calculate the psi in a closed system when the container is heated.
  10. L

    Internal energy of a gas and kinetic energy, "typical velocity"

    Source: Shankar Yale OCW physics I have three questions here: 1. K_avg is 3/2kT, sure. But isn't this the kinetic energy of one particle only? So why isn't the answer multiplied by avogadro's number (because one mole). 2. When doing the "typical velocity" derivation, I noticed that they used...
  11. N

    Thermodynamic Work vs Mechanical Work

    At first I thought these values should be equal because I thought thermodynamic work is simply the work done as the gas compresses or expands. That is, the work done as the gas expands ( and the mass gets lifted up) should be equal to the work done against gravity as the mass goes up, and the...
  12. jojosg

    Chemistry Need help with Ideal Gas Question

    Need help solving this question. Can't seem to get the right answer using PV/T=constant P1V1/T1 = P2V2/T2 Patm = 75.23cmHg T1+20+273=293K STP: P=1.01 x 10^5 N/m^2 Pabs=41cmOil P1 = density x g x h = (810 kg/m^3)(9.8 m/s^2)(75.23-41)x10^-2 mOil=2717.18 N/m^2...
  13. J

    Max inversion temperature for a gas (Dieterici’s equation of state)

    The notes my lecturer has provided state that the maximum temperature can be found taking p = 0 in the inversion curve formula, given as: I’m not sure how to obtain this?? These are the formulas: This is my attempt at a solution : Not sure if this approach is right?
  14. G

    Molecular speed distribution - most probable speed V

    Can someone explain to me what I am doing wrong? Trying to calculate the Temperature T using this formula I am trying to find T using most probable speed of atoms formula. T = (V^2) m/( 2k) I am getting riduculous T like 20x10^27. Why? If number of atoms N= 2x10^24 how do i get mass m? each...
  15. Dgasman

    Pressurizing feed gas with venturi

    Gas flow rate: 20lpm Gas: 10% ozone Injected into water Water flow rate: 120GPM Mazzei Injector: 784
  16. Greg Bernhardt

    How to avoid gassing out from snowblower fumes

    After 40 years I finally got a snowblower and wow does it pump out the fumes. Pretty sure I got a high and a headache. Any tips for dealing with this? Anyone wear a vapor mask?
  17. Lotto

    B What is the pressure acting on the air?

    Let us say that the glass isn't whole under the water. If the height of the air layer under the water is ##\Delta x##, then the pressure the water acts on the gas is ##p=p_{\mathrm {atm}}+\Delta x \rho g##. But my confusion is why the "hydrostaic pressure" is ##\Delta x \rho g##, not ##L\rho...
  18. C

    Find the equation of state of each gas

    The problem is from the book "The Principles of Thermodynamics" by ND Hari dass. It looks trivial problem, but I am not able to form logical arguements for going into next step. For example, It seems like first gas has equation of state ##PV =nRT## and second has ## \left( P_2 +\frac{a}{V_2^2}...
  19. gibatom

    Simulation of a gas in 2-D using a Verlet algorithm

    Verlet Algorithm with periodic conditions
  20. Lotto

    What helium mass in a balloon to make it bouyant in air?

    I suppose that the temperature is the same for the helium as well as for the air. So ##\frac 43 \pi r^3 \rho g >m_{He}g+4\pi r^2 \sigma g##. I would determine the density of air from ##p_0 \mathrm d V=\frac{\rho \mathrm d V}{M_a}RT##. So ##m_{He}<4\pi r^2\left(\frac{p_0M_a r}{3RT}-\sigma...
  21. Albo

    Exit velocity of gas through two orifices

    If a gas flowing through a tube would meet two orifices with different diameters in the same cross section, how much of the gas would flow through each orifice and what would the gas velocity be in dependence of orifice diameter?
  22. Aayush Verma

    Effect of relative motion on pressure of gas in a container

  23. J

    A Can Hamson-Linde cycle liquidize N2?

    Hi ! To me it seems linda cycle can not liquidize nitrogen. Please explain me, can it liquidize N2? Here is how I come to this result: Imagine compressor take nitrogen 1bar 300k and gives 200bar hot, but cooled to 200bar 315k. Next n2 is cooled in counterflow heat exchanges (hex) by cool n2...
  24. aliinuur

    I This gas work violates 2nd law of thermodynamics?

  25. M

    Finding gauge pressure for gas inside light bulb as it heats up

    For this 19(a), The answer is 0.137 atm. My working is ##P_{gauge} = P_f - P_i## ##P_{gauge} = \frac{nRT_f}{V_f} - \frac{nRT_i}{V_i}## ##P_{gauge} = \frac{nRT_f}{V} - \frac{nRT_i}{V}## since volume does not change ##P_{gauge} = \frac{nR}{V}(T_f - T_i)## However, I am not sure how to go from...
  26. phos19

    I Fermi energy for a Fermion gas with a multiplicity function ##g_n##

    I ran across the following problem : Statement: Consider a gas of ## N ## fermions and suppose that each energy level ## \varepsilon_n## has a multiplicity of ## g_n = (n+1)^2 ##. What is the Fermi energy and the average energy of this gas when ## N \rightarrow \infty## ? My attempt: The...
  27. chocopanda

    Mixing two gases in an isolated system and calculating final p and T

    Hey everyone, I have an attempt at fully solving this problem (my final pressure is ##p_f = 5373,64 hPa##, final temp. is ##T_f = 303,15K = 30C##), but this exercise confuses me very much. First, I have not used the masses in my calculations and I'm pretty sure my prof. accidentally copypasted...
  28. Saladsamurai

    Predicting Remaining Pressure in Compressed Gas Cylinder

    Well, it's been nearly 10 years since my last post, and it's been about that long since I've thought about ideal gases, so here we go :smile:. Description of Setup I have a system that uses compressed gas cylinders as a source to slowly purge an optical payload. The source is 12x compressed...
  29. F

    I Calculating Pressure Change Filling Gas Cylinders

    I want to work out how to calculate the pressure change in a gas cylinder if it is used to fill another cylinder to a lower pressure. For example, if a 50 litre gas cylinder initially at 200 bara is used to fill a 600 litre cylinder from atmospheric pressure to 1.5 Bara. What would the change...
  30. M

    Why must we use absolute temperature for the Ideal Gas Law?

    For this problem, The solution is, However, why must we use absolute temperature for the ideal gas law (i.e why can we not use Celsius for T) Many thanks!
  31. S

    I So what are the definitions of gas, liquid, solid?

    Obviously, we know intuitively what they mean, but it seems that physicists have developed an objective definition for all of these. If I were to guess, I'd say that: - a gas is vastly less compressible than a liquid or solid (i.e., which are considered in thermodynamics as basically...
  32. confused_steve

    I Force Required for Gas Struts on 1972 VW T2 Danbury Pop top campervan?

    Hi all, i'm the proud owner of a 1972 VW T2 Danbury Pop top campervan. Out of the factory these were fitted with 4 x long spring loaded struts which (when new) provided some lifting power to pop the roof up. Mine are now 50 years old and provide no assistance lifting / holding the roof in...
  33. kakaho345

    Finding free electron gas Green function in Fourier space

    As in title: Plugging in the definition is straight forward, I am too lazy to type, I will just quote the book Fetter 1971: Up to here everything is very straight forward, in particular, since we are working on free electron gas, ##E=\hbar \omega## However, I have no idea how to arrive...
  34. bruhtation

    B Gas cylinder at constant pressure being exposed to atmosphere, how?

    im learning thermodynamics and currently in a lesson about thermal processes. one process has constant pressure and before diving into equations or any proof the book provides a figure of a gas cylinder. the cylinder has a movable piston/lid on one side. the book then says "...and the piston end...
  35. lk0306

    Do these substances emit formaldehyde gas when heated?

    Hey there, Trying to confirm whether or not these substances emit formaldehyde gas when subject to heat of hair straightener and hairdryers. Both were ingredients in a keratin treatment i used at home and i had a crazy reaction (irritated skin, eyes, hair, nose and lungs) in the process of...
  36. M

    Heat exchanged in Expanding and cooling gas

    For part(b), My solution is, ##\Delta E_{int} = Q - W = \frac{3}{2}(P_fV_f - P_iV_i)## ##Q = W + \frac{3}{2}(P_fV_f - P_iV_i)## ##Q = 4000 + \frac{3}{2}((1 \times 10^6)(6 \times 10^{-3}) - (3 \times 10^6)(2 \times 10^{-3})## ##Q = 4000 J## However, according to the solution b. ##−4000 J## Can...
  37. M

    Finding heat exchanged work done to compress gas

  38. M

    Understanding Isothermal Work: Solving the Gas Compression Problem

    For this problem, dose anybody please give me guidance how they got 74 K as the answer? Note that chat GPT dose not give the correct answer (it gives the temperature of the gas is 1500 K). Many Thanks!
  39. M

    Work done on a gas when it is compressed quasi-statically

    For this derivation, I am not sure why the bit highlighted in orange is not positive since the displacement of the piston is downwards in the same direction as the force applied. Many thanks!
  40. Ebi Rogha

    Gas temperature in a constant volume

    An insulated container (constant volume, adiabatic) contains an Ideal gas with pressure P1 and temperature T1. We open the container's hatch for a few seconds and let some particles escape from the container, then we close the hatch again. We know container's pressure has reduced by exiting...
  41. H

    Calculating ΔE Difference for 2 Samples of Monatomic Ideal Gas

    Question: Two samples of a monatomic ideal gas are in separate containers at the same conditions of pressure, volume, and temperature (V = 1.00 L and P = 1.00 atm). Both samples undergo changes in conditions and finish with V = 2.00 L and P = 2.00 atm. However, in the first sample, the volume is...
  42. Y

    A Learning DFT: Inhomogeneous Electron Gas (Hohenberg) Question

    I'm reading through Hohenberg's seminal paper titled: "Inhomogeneous Electron Gas" that help lay the foundation for what we know of as Density Functional Theory (DFT) by proving the existence of a universal functional that exactly matches the ground-state energy of a system with a given...
  43. rogdal

    Gas in a box with Maxwell-Boltzmann distribution

    I have considered two scenarios: 1) A particle that has just collided with the wall at ##z=L## is moving with a velocity ##v_z<0## moving away from the wall. Hence, the probability that this particle has of colliding again is ##0##, so its distribution is also ##0##. 2) A particle moving with...
  44. V

    B Collision time interval of a gas molecule with wall of container

    I have been trying to make sense of the derivation of pressure under Kinetic Theory of Gases chapter, but it's not making sense to me when the impulse momentum equation is used for the collision between a gas molecule and the wall of the container. The book says that for the elastic collision...
  45. S

    I Wall material effect on Van der Waals gas?

    Ref: Van der Waals Equation @ Wikipedia The above paragraph is explains how intermolecular attraction reduces the gas pressure, assuming that there is no attraction between walls and particles. In practice, would there be a change in pressure from one kind of wall to another, if we ensure...
  46. patric44

    Percentage change in the density of a gas

    Hi all, in this question i was asked to find the percentage change in the density, my approach was as following, first i find the change in volume due to putting the gas into the other vessel as: $$ P_{1}V_{1}=P_{2}V_{2}\;\; → \;\;V_{2}=\frac{P_{1}}{P_{2}}V_{1} $$ now i use $$...
  47. P

    Incompatibility between ideal gas equations of state

    To solve this problem I used two equations: $$ PV=nRT, $$ where ##P## is the pressure, ##V##the volume, ##R##the gas constant, ##T##for temperature and is##n##the number of moles, related to the mass ##m## and molar mass ##M## by $$ n=\frac{m}{M}. $$ It will be also necessary consider the...
  48. C

    Pressure in a gas container measured with a barometer and a U pipe

    Can someone please tell me where I am wrong, here goes the question: to a container filled with gas, U shaped pipe is attached, as shown in the picture(picture below). What is a gas pressure in the container if the height of the pillar of mercury in barometer is 740 mm? The way I solved it is...
  49. S P

    As much steam as possible from engine exhaust gas + warm water?

    Hi all, The idea is to generate as much as possible water steam from heat of internal combustion engine exhaust gas. The so called steam generation device is a simple sloped engine exhaust pipe where water from engine cooling and hot gas is fed at the top and all the mix is exiting at the...
  50. dorothy

    Temperature & Gas: Correct or Incorrect?

    (1) Incorrect, since the root mean square speed(c^2）is directly proportional to the temperature, but it will just affect the average kinetic energy, doubling the k.e., but not related to the potential energy. (2) Correct, since the volume of gas is directly proportional to the temperature (3)...
Back
Top