Gases Definition and 501 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.

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  1. P

    Why does 'breaking' not occur in liquids and gases?

    I'm not exactly sure whether this qualifies as quantum mechanics, but it has to do with how atoms work: suppose a glass plate falls and breaks (into two pieces, let's say, to keep things simple) on the floor. Is it possible to put it back together so that there is no longer a crack between the...
  2. S

    Maximum work obtained by mixing 2 gases

    Homework Statement 2 boxes containing the same number of moles of 2 ideal identical gases with the same adiabatic index (this is given as gamma), at the same initial temperature Ti but with different volumes, V1 and V2 are brought together. Find the maximum mechanical work that can be obtained...
  3. T

    What gases are not able to be collected over water due to their solubility?

    Homework Statement In a proper laboratory setup for collecting a gas by water displacement, which of these gases could NOT be collected over H2O because of its solubility? A. CO2 B. NO C. O2 D. NH3 E. CH4 Homework Equations - The Attempt at a Solution I know E is definitely wrong because its...
  4. samjohnny

    Phase Boundary between mono and diatomic gases

    Homework Statement Consider a gas (note: treat as ideal) that has phase coexistence between diatomic and monatomic forms at ##T_0## and ##P_0##. Compute the equation for the P,T phase boundary between monatomic and diatomic gases. Homework Equations ## u_v (V,T) = \frac{5}{2} RT -...
  5. Ecthe

    Rare gases : calculating absorption by oscillator strength

    Hello, I have some papers (I can give references if needed) giving the oscillator strength of rare gases for a given energy bandwidth and from those values, I would like to calculate their absorption in those bandwidth. However, I am a little bit lost in how to do it. I looked a bit around and...
  6. E

    Kinetic Theory of Gases- no. of collisions

    Homework Statement One mole of oxygen at 27°C and at one atmospheric pressure is enclosed in a vessel. Assuming the molecules to be moving with Vrms, find the number of collisions per second which the molecules make with 1 m2 area of the vessel wall. Homework Equations vrms = √(3RT/M) PV = nRT...
  7. A

    I If air is a mixture, why don't the gases separate?

    If you try to mix water and sand, the sand will mix around and eventually fall to the bottom. Sand and water can't make a solution, so they separate. However salt and water can make a solution, and they don't separate. If air is a mixture, why don't the gases separate? 1) So, pretty much what...
  8. J

    Finding volume ratio between 2 vessels using ideal gases

    Homework Statement I have been tasked with designing a feasible experiment to determine the ration between 2 vessels. I think i have a way that works on paper. Homework Equations pV = nRT and the conservation of mass. The Attempt at a Solution 1.Start with 2 vessels of unknown volume x and y...
  9. TheSodesa

    Find out the molar fractions of all the involved gases

    Homework Statement [/B] 5,00 moles of graphite and 5,00 moles of oxygen gas are stored in a metal bottle. The temperature is raised until the graphite starts burning. The burning produces a mixture of CO and CO2 gases in the vessel. After the temperature had returned to it's original value...
  10. K

    Q and W for Van-der-Waals Gases

    Homework Statement I have the following task: Homework EquationsThe Attempt at a Solution I already managed to calculate Delta Um, but how do I calculate Q und W. Can I use the equations for the isothermic expansion for ideal gases, even if this are Van-der-Waals Gases?
  11. J

    Ideal Gas Law: Doubling Temperature and Volume

    Homework Statement Homework EquationsThe Attempt at a Solution I chose 1&2, but all three are correct. I thought for a constant pressure, if temperature is doubled, then the volume would doubled too? As P=V/T ?
  12. Karan Punjabi

    Molecule Size VS Occupied Volume of Gases

    Ar STP Every gas occupies same volume of 22.4 L but how it can be because every gas molecule has different size right? So they should occupy different volumes right? If I'm wrong at any point then please correct me
  13. E

    Flow of gases through a capillary

    You have a capillary with a stream of water vapor flowing through. Inside the capillary argon gas is also flowing (in the same direction) with a flow rate of 3 L/min. How high of a flow rate can the water vapor have before it starts condensing on the walls? Flow is laminar and the system is at...
  14. B

    Physics: pressure of mixing gases

    Homework Statement 96 grams of oxygen and 50 grams of hydrogen gas occupy separate, equal sections of 200 liter tank. The divide is removed and the gases are allowed to mix and react with each other. Temperature is kept constant at 120 degrees celsius 2. Homework Equations [/B] b) find the...
  15. R

    Helium vs Argon: Cost as shielding gases

    Intuitively I always thought He was more expensive than Ar as a shielding gas. But I was reading this book about Heat Exchanger Design & it has this quote that claims "Argon is costlier than Helium" (Link below; see Bullet Point...
  16. A

    Calculation of absorption coefficients of gases at moderate temperatures

    Hello chaps, I'm trying to calculate absorption coefficients of gases at moderate temperatures ie ranges in which diatomic gases (such as N2 orO2) are partially disassociated or ionised, therefore including molecular bands as well as continuum. Can anyone recommend some suitable reading...
  17. Q

    Why do different gases have different densities?

    I've read that gas molecules do not have any attractions or regulations between them... So why do different gases have different densities?
  18. pvp042

    Electromagnetic effect on gases

    Are there any research or paper regarding electromagnetic effect on gases. For example does H2 gas physically move under electromagnetic field?
  19. S

    Gases compression at critical point. LNG (Methane) storage.

    There are claims or at least assumptions that: "upon approaching "critical point" pure gases become super compressible. You could compress them many times without pressure increase and store like this if you maintain exact temperature and pressure needed. It opens possibility to superdense gas...
  20. woa12

    A Hypothetical Situation Involving Gases

    What would happen if all of the empty space of the universe from the small to the vast, were replaced with the gases that make the Earth's atmosphere while neglecting gravity from any massive object?
  21. J

    Solving Ideal Gas Problem: Find # of Balloons Filled

    Homework Statement A gas cylinder contains 4x10^4 cm cubed of hydrogen at a pressure of 2.5x10^7 Pa and a temperature of 290 K. The cylinder is used to foll balloons. Each balloon contains 7.24x10^3 cm cubed of hydrogen at a pressure of 1.85x10^5 and a temp of 290K when full. Find the number...
  22. S

    Why Is Time Represented as 2d/v in Kinetic Gas Theory Calculations?

    To obtain force from momentum we use the formula change in momentum/time. The time in the equation refers to the amount of time the force is exerted on the gas molecules. So when considering the kinetic theory of gases we are taught that F ∝ change in momentum/ time so F ∝ 2mv/(2d/v) and hence...
  23. L

    Specific heat capacity of gases

    Homework Statement Figure shows two rigid vessels A and B, each of volume 200 cm3 containing an ideal gas (Cv = 12.5 J/mol-K). The vessels are connected to a manometer tube containing mercury. The pressure in both the vessels is 75 cm of mercury and the temperature is 300 . (b) 5.0 J of heat...
  24. mooncrater

    Pipes, resonating frequencies and yeah some gases

    Homework Statement A closed organ pipe resonates in its fundamental mode at a frequency of ##200Hz## in ##O_2## at a certain temperature. If the pipe contains 2 moles of ##O_2## and 3 moles of ##O_3## are now added to it, then what will be the fundamental frequency of same pipe at same...
  25. AdityaDev

    Is the rise in mercury level due to a change in pressure or temperature?

    Homework Statement A tube which is open at both ends is immersed in a beaker containing mercury. The top end which comes out of the mercury level is now sealed and then the tube is raised by some height such that some part still remains inside the beaker. The mercury inside the tube rises...
  26. I

    Temperature and entropy for two gases mixing

    Homework Statement A system is made up of two halves. In one there's 10kg neon gas with the temperature ##20 \circ##C, in the other 10kg nitrogen gas with the temperature ##100 \circ## C. Suppose the septum is removed so that thermodynamic equilibrium may appear and the gases mix. Calculate...
  27. J

    Electrons & Gases: Changing Colour w/ Speed Increase

    What type of gas would change the colour of an electron beam as the speed of the electrons increases?
  28. B

    Gases I could expect to see using an IR receiver

    Hi I was wondering if someone could tell me what kind of gases I could expect to see using an IR receiver between the wavelengths of 110 and 330 nm. As well as this id love to know what kind of glass could be used in order to not interfere with the actual results. Thanks a million
  29. P

    How can I remove steam from exhaust gases?

    hello I have hot gases with steam (water) inside how do I separate it ? without cooling it magnetic field can help? ultrasound? something else? thanks!
  30. L

    Delta(U) = Cvdelta(T) for Ideal Gases?

    I don't understand how Delta(U) = Cvdelta(T) is always true for Ideal Gases...Shouldn't this only be true for constant volume processes? Yet it seems to be used even when a gas is expanding or being compressed... Any ideas...Thanks in advance.
  31. J

    Kinetic Theory of Gases Derivation

    Hi, I am struggling with a particular point on the derivation of the kinetic theory of gases. Between 5mins and 6mins 30seconds of the video below they discuss how to get a value for the average of the squared velocities of the molecules in the gas. The bit I don't get is why they divide by 'N'...
  32. Robin04

    How can the radiation of gases be detected?

    I'm curious about that do gases emit infrared radiation the same way as solid bodies do? If yes, how can it be detected like an infrared camera does?
  33. K

    Finding average angle in kinetic theory of gases

    Homework Statement "Show that particles hitting a plane boundary have traveled a distance 2λ/3 perpendicular to the plane since their last collision, on average."Homework Equations (Root mean path squared) <x> = 2^(.5)λ λ = ( 2^(.5) * n * sigma )^(-1) ANSWER: The Attempt at a Solution...
  34. patrickbotros

    Why is Delta S purely dependent on gases?

    My teacher constantly stresses that 10 moles of a gas going to 11 moles of a gas will ALWAYS cause an increase in entropy (ΔS>0). But why? For example (I know that O2 shouldn't technically be a liquid, but just as an example): 2H2O(g)⇔H2O(g)+(3/2)O2(l)+2H2 It seems iffy to me. We go from...
  35. I

    (Gases) How to get dU=(PdV+VdP)/(gamma-1) from U=PV/

    Hello I'm reading Feynman here: http://www.feynmanlectures.caltech.edu/I_39.html I'm having problems understanding how he turns equation 39.11 into 39.12. He does some U -> dU trick and he turns: U=PV/(\gamma-1) into dU=(PdV+VdP)/(\gamma-1) I don't understand this intuitively. Any help...
  36. AdityaDev

    Speed of sound in mixture of gases

    I am trying to calculate the speed of sound in a mixture of 2 gases like oxygen an ozone. First step: I calculated ##\gamma_{eff}## of the mixture by first calculate the ##C_V## of mixture by using a formula $$C_V=\frac{n_1C_1 + n_2C_2}{n_1+n_2}$$ Step 2: in the formula $$v=\sqrt{\frac{\gamma...
  37. Logan Land

    Classical gases not necessarily ideal

    Systems A, B, and C are classical gases (not necessarily ideal), each with the same number of molecules N ( or same number of moles n if you prefer), where N is constant. We can measure pressures and volumes Pa,Va ; Pb,Vb ; and Pc,Vc for each system. When A and B are in thermal equilibrium, our...
  38. Logan Land

    MHB Classical gases not necessarily ideal

    Systems A, B, and C are classical gases (not necessarily ideal), each with the same number of molecules N ( or same number of moles n if you prefer), where N is constant. We can measure pressures and volumes Pa,Va ; Pb,Vb ; and Pc,Vc for each system. When A and B are in thermal equilibrium, our...
  39. Symmetry777

    Dielectric Constant Chart of Gases

    Is there a creditable chart out there - on the dielectric constant of gases? What is the dielectric constant of Sulfur hexafluoride (SF6) compared to other gases or other gases in a vacuum? Thank You
  40. N

    Heat Recovery from Boiler Exhaust Gases

    Homework Statement The exhaust gases from a natural gas-fired central heating boiler leave the boiler at a temperature of 70 deg C. The oxygen content of the exhaust gases is 9% by volume (dry). The rate of energy input (Gross calorific value) to the boiler from natural gas is 16kW. The gross...
  41. N

    Gasoline smell does not inginte

    Say there is a chair soaked in gasoline. If someone is to walk in the room the smell is immediate if the chair was lit on fire the liquid gasoline would ignite the chair. However, what about the particles that constitute the smell of it? Why don't they ignite as well? What is the nature of the...
  42. P

    Unravelling the Mystery of Rare Gases and Binding Energy

    Hi! I saw something on my lecture notes that I don't really understand. It reads "Rare gases have filled s and p-sub-shells, which leads to a spherically symmetric charge distribution. Since electrons are indistinguishable they take on a common wavefunction. The point is that this results in a...
  43. M

    Calculating Particle Energy Loss in Gases: Where to Start?

    Hey guys, Im currently looking for a way to calculate the energy loss of a particle in a gas. This will help me to understand deposition processes better. The particles I am looking at are heavy, uncharged ones (e.g. metal atoms). Stopping power is not a viable concept without charge, and Bethe...
  44. Drakkith

    Volume of Two Gases: Does Adding Apply?

    I had an exam question where I had to find the volume taken up by a gas consisting of 32 grams of oxygen and 4 grams of helium at STP conditions. I ended up getting a supposedly incorrect answer of about 44.8 liters by finding the volume of both gases and adding them together. However, my...
  45. R

    Thermodynamics : molar specific heats for gases

    Homework Statement An audience of 2750 fills a concert hall of volume 35000 m3. If there were no ventilation, by how much would the temperature of the air rise over a period of 2.0 h due to the metabolism of the people (70 W/person)? Homework Equations Q= nCvΔT Cv= (3/2) R The Attempt at a...
  46. K

    Thermodynamics: 2 gases in 2 chambers

    Homework Statement A stiff and isolated vessel is divided into 2 halves by an isolator divider. in each half there is a gas (i am not told if it's the same) with presures and temperatures T1, P1 and T2, P2. the divider is removed. Apply the first law of thermodynamics and draw conclusions...
  47. M

    Calculating Final Outlet Temp of Flue Gases

    Homework Statement If the flue gases exiting the boiler are used to preheat the water fed to the boiler from a temperature of 28 C to 90 C and assuming: • a mean specific heat capacity for water over this temperature range to be 4.2 kJ kg–1 K–1 a mean molar heat capacity for the flue...
  48. V

    Newton's First law and KT of Gases

    One of the assumptions of Kinetic Theory states that: A gas is a substance composed of many particles flying about randomly, colliding with one another and with the walls of the container. My instructor mention that we might be required to Know, state, and apply this theory to one of newtoms...
  49. V

    KT of Gases and static equilibrium

    In a recent class, my instructor covered the Kinetic Theory of gases. My question is in regard to the theory which states 1) The size of the individual molecues in a gas are so small that their volumes can be considered negligible. The instructor then mentioned that the paticles in the gas can...
  50. P

    The propagation of disturbances in interstellar gases

    Homework Statement Show that the solution of the form ρ1 = ρ1(x±a0t) satisfy the equation: ∂2ρ1/∂t2 - a02∂2ρ1/∂x2 = 0 and that they correspond to waves propagating in the directions x increasing or decreasing. Homework Equations P = P0 + P1 ρ = ρ0 + ρ1 u = u1 The Attempt at a Solution P1 =...
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