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. T

    Why does the pressure of a gas bubble change as it rises?

    The correct answer is 'C'. I'm having trouble understanding the solution shown on this link (http://www.engineeringadmissionsassessment.com/2019-solutions.html) - scroll down to Section 2, Question 8. From what I've gathered, [final pressure = initial pressure x 'R^3/r^3'], as PV must be...
  2. K

    Proof question related to the Ideal Gas Law

    A cylinder contains an initial volume V1 = 1m^^3 of a perfect gas at initial pressure p1 = 1 bar, confined by a piston that is held in place by a spring. The gas is heated until its volume is doubled and the final pressure is 5 bar. Assuming that the mass of the piston is negligible and that the...
  3. WMDhamnekar

    MHB Maths in Temperature and ideal gas Thermometer

    Hi, I didn't understand the maths involved in the below article in regard to temperature and ideal gas thermometer. If any member knows it, may reply me. If triple point of water is fixed at 273.16 K, and experiments show that freezing point of air-saturated water is 273.15 K at 1 atm...
  4. K

    Finding the Volume of an Ideal Gas

    Hi, I tried to do this question in two different approaches one of them was using the equation PV=mRT where I got the right answer which is 4.305 m**2. However, I tried using this Density = Mass/Volume, where I substituted Denisity= 1.225 and Mass equals 5kg to get the volume as 4.08. Can...
  5. WMDhamnekar

    MHB What is the final pressure of helium and neon gas mixture in this case?

    The answer given to the above question is Final pressure$=\frac{(10.0mol\times 5.00bar) + (5.00 mol \times 20.0 bar)}{(10.0 mol +5.00 mol)}= 10.0 bar$ Is this answer correct? if yes, How and why? My question is while computing this answer, the volumes of each gas is not considered. Note:-...
  6. J

    Chemistry Ideal Gas Law and Partial Pressures

    I had already found the Mass of the product (C3H3N) produced by this reaction (theoretical mass at 100% yield) in a previous problem. I did this by finding the Limiting Reagent (C3H6) in the reaction , calculating the number of moles of C3H6 and using the Molar Ratios in the balanced reaction...
  7. A

    Ideal gas: two tanks connected by a cylinder

    I ASSUME THAT THE PRESSES OF THE TWO CONTAINERS WILL BE EQUAL IN THE FINAL (STATIONARY REGIME). SO Pa = Pb naRTa/V = nbRTb/V naTa = nbTb Than , I just need to set up a system My question is , so, will the two pressures at the end be the same? And as for the temperatures, can I also say...
  8. S

    Number of balloons that can be filled from a gas cylinder

    ##\frac{P_{cylinder}.V_{cylinder}}{P_{balloon}.V_{balloon}}=\frac{n_{cylinder}.R.T}{n_{balloon}.R.T}## ##\frac{n_{cylinder}}{n_{balloon}}=\frac{4 \times 10^4 \times 2.5 \times 10^7}{7.24 \times 10^3 \times 1.85 \times 10^5} \approx 746## But the teacher said I should take the volume of gas...
  9. jk22

    B Why expansion of a gas implies cooling?

    Normally expansion implies colding, but I don't know how to explain this with the equation of perfect gazes : ##PV=nRT## If V increase then the pressure diminishes. Admitting a constant number of molecules, is the number of shocks is inversely proportional to the volume ? But this only implies...
  10. Z

    Question regarding the Pressure of a gas flowing from a cylinder into balloons

    P1V1=P2V2 (2.5x10^7x4x10^4)/1.85x10^5 , V2 = 5.41x10^6 cm^3 5.41x10^6=4x10^4+7.24x10^3 N N= 741
  11. U

    Chemistry Calculating Mass Percentage of N2H4 in Hydrogen/Nitrogen Mixtures

    So essentially you are supposed to find the mass percentage of N2H4 in the Hydrogen/Nitrogen mixtures. The way I understood it, the only way to find the mass percentage of the gasses is to find the mole percentage. Which I got as 25%, based on the fact that the ratio of product gasses to...
  12. P

    Relationship between Cp, Cv and R

    According to me a=b cause what I have been learning is R is gas constant and hence it will be same for both. But the solution have says something else. According to them Cp-Cv=R/M where M is the molecular mass of gas. So is the above mentioned formula correct? Do we have to take that M term...
  13. sophiecentaur

    Old fashioned gas stove with automatic lighting - how?

    I cleaned the two ovens in our conventional gas stove. They light themselves - trying a few times if the flame doesn't strike and give up if no dice. One of the ovens would strike and light, then go out and try again - clunk pause clunk pause etc. I decided to have a look at the burner unit as I...
  14. Hiero

    Adiabatic expansion of a piston in a cylinder filled with ideal gas

    I was puzzling over how to solve this and finally peeked at the solution. They used the relevant equation above. I disagree with this though. The problem specifically says “the piston is allowed to slide freely!” This means that we don’t let it happen slowly. So then we are not in...
  15. K

    How does an LPG tank gauge work?

    Hi I have read that the propane gas tank gauges that rely on pressure are useless because as you use the tank part of the liquid propane turns to gas raising the pressure again inside the tank. What id like to know is then how do these gauges work? And also I would like more detail on how...
  16. T

    Divergent nozzle for releasing pressurised gas

    I have air/gas pressurised gas (pressure is 7 barG). I want to know what are the parameters of the divergent nozzle needed so that the pressurised gas can be released to atmospheric pressure level smoothly and necessary enthalpy conversion can be achieved i.e. the air/gas will accelerate to its...
  17. L

    I When does the ideal gas equation break down?

    P1/V1/T1 = P2 V2 /T2 is derived from the ideal gas equation. However it is stated that this equation breaks down at very high pressures and at very low temperatures. Does anyone know what kind of pressures and temperatures we are talking about here?
  18. E

    B What is the significance of Δx and Δp in the ideal gas entropy equation?

    Up to an undetermined constant ##a## the entropy of an ideal gas goes like$$S = k_B N\ln \left[ a^\frac{3}{2} \left(\frac{V}{N}\right) \left(\frac{E}{N}\right)^{\frac{3}{2}} \right]$$In some notes is written: And then they identify ##\Omega = \left(\frac{\Delta x \Delta p}{w}\right)^{3N}##...
  19. E

    B Calculating Flow Rate for Air and Methane in a Valve

    good day! I did not find a suitable forum thread, so I am writing here ... There is a valve through which you need to drive gas under a certain pressure, physically there is no way to drive gas, so it was decided to replace the gas with air. Knowing the required pressure and gas temperature, how...
  20. C

    Engineering Calculate valve sizing to regulate the flow of natural gas

    Working out as follows x= (20-6)/20 = 0.7 Fk = k / air specific heat ratio Fk = 1.31/1.4 Fk = 0.94 xT = Fk * x 0.94 x 0.7 = 0.658 because xT < x = 0.658<0.7 flow through the valve is choked Expansion factor Y Y = 1 - x/( 3 x Fk x xT ) Y= 1- 0.7/( 3 x 0.94 x 0.658) Y = 0.623...
  21. Sabertooth

    A Relativistic Effects on Particles and Gases

    Hello everyone, I was doing some calculations recently regarding particle velocities for different elements at different temperatures and I have a few questions for the experts in here. Usual gas laws in my school book provides information about the velocity of particles in gases, it provides...
  22. George Keeling

    I Questions about spaghettification and gas cloud G2

    I did an exercise about beacons falling radially into black holes from Carroll's book and got a formula for the proper velocity$$ \frac{dr}{d\tau}=-\sqrt{\frac{R_S}{r_\ast}}\sqrt{\frac{r_\ast-r}{r}} $$It's in natural units (##c=1)##, ##r_\ast## is where the beacon is dropped from and ##R_s=2GM##...
  23. Like Tony Stark

    Determine the heat capacity at a constant volume for a Van der Waals gas

    Hi, what I've done so far is solving equation 2) for ##U##, and replacing what I get in equation 1). Then, ##c_V## is equal to the partial derivative of ##S## with respect to T times T, so I've done that. The derivative is ##CNR/T##, so ##c_V=CNR## but those aren't the correct units for ##c_V##.
  24. Amirul96

    Mass and Volumetric Flow rate of Natural Gas

    Hi. I am currently doing my internship in the oil and gas industry (contractor) as process engineer. My supervisor give me a task to do some reverse engineering where i need to study how a spreadsheet (calculation) construct by other process engineer was been constructed. Ok the situation is the...
  25. L

    GridTie Synchronous Generation Project Using Carbon Neutral Flare Gas

    Details to follow if there is interest.
  26. L

    Liquid Diamonds: A Mystery of Gas Giants

    Liquid diamonds apparently may form in gas giants where huge atmospheric pressure compresses carbon into diamonds that are then liquified as they fall downward into zones of increasing pressure. I thought a diamond was a crystal structure of carbon. How can this also be a liquid...
  27. P

    Finding the efficiency of an ideal gas with adiabatic exponent 'γ'

    Here is what I did : work done in going from A to C, W1 = 2nRToln(2) (isothermal process) work done in going from C to B, W1 = pΔV = nRΔT = -nRTo (isobaric process) work done in going from B to A, W3 = 0 (isochoric process) so, total work done = W1 + W2 + W3...
  28. C

    Van der Waals Gas: Properties & Uses

  29. V

    Ultra Relativistic Free Electrons Gas

    I don't know how to approach this problem.
  30. A

    Temperature is a measure of the average kinetic energy of a gas?

    Why do they say temperature is a measure of average kinetic energy how is this possible. how can we take it is it applicable for all types of gases?
  31. Jehannum

    Problem / conflict with gas appliance ventilation standard

    Unflued gas appliances emit all of their combustion products into the room in which they are installed. In the UK, ambient carbon dioxide in the commercial workplace is limited to 2800 ppm. The UK/European standard BS EN 13410 (and many appliance manufacturers) give the formula for mechanical...
  32. G

    A rocket and its gas exhaust velocity

    This isn't right, is it? -\dfrac{GM}{R}+\dfrac12 v^2=-\dfrac{GM}{R+h} v=\sqrt{\dfrac{GM}{R}}\left( 1-\sqrt{\dfrac{R}{R+h}}\right) He's doing energy conservation. The mechanical energy at the Earth's surface is equal to the energy when the speed is 0.
  33. greg_rack

    Maxwell-Boltzmann distribution for the simulation of a perfect gas

    I'm currently programming lots of physics simulators in DHTML, and my next step would be simulating a perfect gas behavior at a molecular point of view, bouncing inside of an HTML canvas. For this reason, I came across "Maxwell-Boltzmann's law of distribution"(for speed, which I only studied...
  34. domingoleung

    Gas in a syringe being compressed - thermodynamic processes

    1. Adiabatic compression (When compressed quickly, there is no heat flow to the environment Q=0) Isochoric with heat loss (The syringe is still compressed, there should be no change in volume) Adiabatic expansion (When the syringe is released, there is work done only) Isochoric with heat gain...
  35. A

    Gas - cylinder - piston problem

    Summary:: Seeking explanation to classical gas - cylinder - piston problem, not the solution. Problem 1.15 from 7th edition of Introduction to Chemical Engineering Thermodynamics by Smith, Van nes and Abbot) Classical problem, given: - gas in a confined cylinder - piston with weight is placed...
  36. A

    Is Entropy decreased for Free expansion of a Waals gas?

    Previous of this problem, there was another problem. that is "What is the change in Temperature of van der Waals gas in free expansion?". I got them. It was C_V dT= -aN^2/V^2 dV Then, I got T=T0-aN^2/2VC_V So i knew that the Temperature is decreased by free expansion in adiabatic process. Then I...
  37. I

    Chemistry What are the partial pressures of each gas in the mixture?

    I've first calculated the partial pressures of each gas: ##N_2: 0.4\times 7.4\times 10^4=3.0\times 10^4 Nm^{-2}\\## ##O_2: 0.35\times 7.4\times 10^4=2.6\times 10^4 Nm^{-2}\\## ##CO_2: 0.25\times 7.4\times 10^4=1.9\times 10^4 Nm^{-2}\\## From here, I do not know how to continue. Could someone...
  38. rjomega

    Effect on Volume of a Change in the Pressure of Compressible Gas

    Will the available Volume of oxygen gas for use of patients increase when the pressure decreases from 12.4 MPa to 500 KPa? Is using boyle's law the right way to calculate the available volume?
  39. Saptarshi Sarkar

    I Query regarding Fermi Gas model

    I was reading an introductory text on nuclear models and came across the Fermi Gas model. I understand that the depth of the potential well of the proton should be less than the depth of the potential well of the neutron due to the Coulombic repulsion between the protons. But I did not...
  40. M

    I How Is Entropy Calculated in an Irreversible Gas Expansion?

    Hi, An irreversible gas expansion is often described in textbooks with a compressed gas in a cylinder pushing up a weight (with mass m) via a hypothetical friction-less and weightless piston. It is said the work done by the gas is equal to -mg × h and from this you can derive the work for a...
  41. L

    Can Ultrasonic Sensors Accurately Measure Gas Tank Levels?

    Hi Folks, I am exploring using Ultrasonic for LGP tank level measurement. I went through lots of readings, in particular use of SRF02 sensor. But, It's not conclusive. Anyone has been exposed to solving such problem? If yes, kindly share return on your experience. Appreciate!
  42. G

    How to think about entropy microstates/macrostates for a gas in a box

    I'm trying to relate an analogy from Brian Greene about entropy microstates/macrostates to the real world. In the analogy, you have 100 coins that you flip. The microstate is which particular coins landed heads up. The macrostate is the total number of coins that are heads up. So a low entropy...
  43. J

    How can hydrogen gas can be made to emit photons of different energies

    This above is the diagram I'm not too sure about the solution to this problem as to why I came here. Is it something to do with photons having different frequencies i.e emitting different amounts of energy based on its frequency
  44. Geith

    (Fluid mechanics) How to find the flow rate of a gas from a vessel

    I am working on a project where I have to calculate various results relating to the motion of a water bottle rocket being launched. I am currently stuck on trying to find how long the thrust period of the rocket is. The model for the rocket is as follows: It is a 2L (0.002m3 bottle filled with...
  45. A

    Specific heat of a monotomic gas

    Given this problem I have calculated the partition function as $$z=1+e^{-\beta E_1}$$ And calculated the average internal energy as $$<U>=\frac{E_1 e^{-\beta E_1}}{1+e^{-\beta E_1}}$$ And thereafter taking the partial derivative of <E> with respect to temp. T the specific heat obtained is...
  46. vis viva

    What happens to cations and electrons during and after a gas discharge event?

    As I understand both cations and electrons are produced between cathode and anode in a gas discharge, but what is their imminent fate, during and post discharge event? The majority of information I could find only covers the electrons from the time of the first ionization event to impacting the...
  47. 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...
  48. Kaushik

    The van der Waals Equation: What is the exact meaning of 'volume of gas'?

    It is said that, for real gases at high pressure, the measured volume is higher than the calculated volume. My perception of the volume of the gas, as of now, is the following: The free space available for the gas to move. It excludes the volume of the molecules. So on increasing the pressure...
  49. C

    Thermodynamics help please -- Air passing through a gas turbine system

    Summary:: NO TEMPLATE BECAUSE THIS HOMEWORK PROBLEM WAS MISPLACED IN A REGULAR FORUM Cant do part c, using the steady flow equation I am confused how to continue. Please help! Mainly confused as to what heat transfer loss represents in the steady flow equation and where to go to find the...
  50. shadedvertex

    Flaw in alternative approach to determine ideal gas speed distribution

    If we assume the energy of particles in an ideal gas follows a Boltzmann distribution, then the energy distribution function can be defined as below: , where k_B is the Boltzmann constant Since the energy of particles in an ideal gas are assumed to only consist of translational kinetic energy...
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