What is Gases: Definition and 501 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. dRic2

    Viscosity and thermal diffusivity in liquids and gases

    Hi PF, I was wondering about this for some time and I can get my head around it. Viscosity ##\mu## is a "measure" of the momentum flux Thermal diffusivity ##\alpha## is a "measure" of the heat flux (kinetic energy of molecules) In gases both viscous stresses and heat flux take place due to...
  2. rpthomps

    I Noble Gases vs. Halogens: Which Has a Greater Atomic Radius?

    Does the noble gases have an atomic radius decrease or increase from halogens?
  3. Amaterasu21

    B Archimedes' Principle for gases - derivation?

    Hi all, I understand where Archimedes' Principle comes from in liquids: If we imagine a cylinder immersed in a liquid of density ρ whose cross-sectional area is A and whose top is at depth h1 and whose bottom is at depth h2: Force(top of cylinder) FT = ρgh1A Force(bottom of cylinder) FB =...
  4. ZiHao

    Pressure in Gases: Boiling Water in a Can Explained

    A teacher heats some water in a drinks can until it is boiling and steam comes out of the can. She quickly turns the can over and puts it into some water. Explain in detail why the can collapses. My solution will be: By boiling the water, the water changes state from liquid to gas, which is...
  5. axer

    Chemistry AvLaw - Which is the correct method of finding moles of gases?

    Homework Statement Based on your understanding of Avogadro's law. 1000 L steel storage tank contains 88.5 kg of methane gas, CH4. Calculate no. of moles. The Attempt at a Solution one method= no. of moles=mass/molar mass. no. of moles= 88500/16.04= 5517.4 moles.other method= 1 mol= 22.4 liter...
  6. L

    Do ideal gases move at the same speed?

    I've learned that ideal gases have the same average kinetic energy, but this doesn't necessarily mean that they have the same speeds within a container..Instead, is it right to say that (according to kinetic molecular theory) that the speed of molecules at an instance is a wide range of speeds?
  7. M

    Noble gases don't react chemically with other substances

    I would like to ask about a question concerning noble gases. "Nobel gases don't react chemically with other substances." Is this statement about nobles gases completely correct or partially correct? Thank you Self made
  8. D

    Specific heat of diatomic gases and equipartion energy

    My doubt it is simply if have other reason to don't use this principle for the specific heat of diatomic gases. Homework Equations $$U=NkT=nRT$$ $$u_n=\frac{U}{n}=RT\text{ molar energy}$$ $$u_N=\frac{U}{N}=kT\text{ average energy}$$ $$Z=\sum{e^{-\omega_i/kT}}\text{ with $\omega_i$ particular...
  9. yrjosmiel

    Does the Kinetic Theory of Gases have an analog for solids?

    And if I can extend this further, for liquids?
  10. D

    Equilibrium volume of two differential van der Waal gases

    Homework Statement Two ideal van der Waals fluids are contained in a cylinder, separated by an internal moveable piston. There is one mole of each fluid, and the two fluids have the same values of the van der Waals constants b and c; the respective values of the van der Waals constant ''a'' are...
  11. G

    Two gases separated by a piston

    Homework Statement [/B] Two ideal gases are contained adiabatically and separated by an insulating, fixed piston that blocks the molecules of gas 2 but allows the molecules of gas 1 through(in both directions). The initial pressures, volumes, temperatures and number of molecules on each side is...
  12. Amaterasu21

    Kinetic theory of gases: rebound speed and force questions

    Hi everyone, I remember years ago at school memorising the derivation of the formula for pressure in the kinetic theory of gases, as explained in this Youtube video: Thinking a little more deeply about this derivation there are two things I don't get: 1) At 0:53, the video says the molecule...
  13. Timothy Schablin

    Work Done By Gases - Calculating Pressure, Volume & Heat

    <Moderator's note: Moved from a technical forum and thus no template used.> Consider a gas in a closed container with a piston allowed to move. Let's start with a volume of 15 and pressure of 1.5. We add heat to the system, let's say 1200 J. This forces the piston to move increasing the volume...
  14. John Dalton

    B What is the atmospheric pressure on Pluto and how can it sustain gases?

    The New Horizon reached Pluto in April of previous year. It shown that Pluto's surface contains mixtures of various gases , such as CH4 and gaseous H2SO4. Now , the query of mine is that- Pluto is situated very far from Sun and is very cold. Please someone justify me how can this gases be...
  15. M

    Do greenhouse gases need to be polar?

    Hi, I have been wondering if greenhouse gases always need to be polar molecules. Can a gas also absorb energy, and heat up, without being polar?
  16. J

    Condition for condensation from adiabatic expansion

    Homework Statement I'm stuck on part (c) of this question. Homework Equations $$T\frac{d}{dT}\bigg(\frac{L}{T}\bigg) \equiv \frac{dL}{dT} - \frac{L}{T}.$$ Clausius-Clapeyron equation: $$ \frac{dp}{dT} = \frac{L}{T\Delta V} \approx \frac{L}{TV_{vap}}.$$ The Attempt at a Solution My approach...
  17. grandpa2390

    Graphing the Gibbs free energy of mixed gases

    Homework Statement I am needing to graph the Gibbs free energy of mixed gases to determine the range when the gases will form an ideal mixture The two gases have the same Gibbs free energy. Homework Equations ##G = (1-X)G_A + XG_B## for unmixed ##G = (1-X)G_A + (X)G_B + RT(x*ln(x) +...
  18. ThunderLight

    B What is the Quantum of Sound in Gases and Air

    It is usually referred to as Phonons for sound waves in solid. But, where it gets confusing, is in gases and air. Some still call it Phonons, others say, Phonons can only be used in solid states. So what is the Quantum of Sound in Gases/Air? And if possible, refer to any text which speaks of...
  19. rodv92

    Decreasing gas breakdown distance in a spark gap with UV

    Hello ! I am currently investigating a technique that would allow several spark gaps to breakdown synchronously in an enclosed but not hermetical cavity, flushed with N2 at 1atm and ~25°C My idea was to use "indirect" photoionization (basically a synthetic fused quartz UV flash discharge inside...
  20. T

    Is nitrogen at 27˚C and 100 kPa an ideal gas?

    Hello everyone. I stumbled across a problem while studying for my exam that I cannot confidently answer. Can we assume nitrogen at the temperature of 27˚C and the pressure of 100 kPa an ideal gas? Justify your answer. The definition of an ideal gas is "...a gas whose molecules are spaced far...
  21. R

    The Effect of Intermolecular Forces on Ideal Gas Behavior

    I read from a website that Most gases behave like ideal gases at many temperatures and pressures. and we have learned that the gases behave like ideal one only in high temperature and low pressure . so which one is true .
  22. blackdranzer

    Entropy change : pure mixing of gases

    Consider three identical boxes of volume V. the first two boxes will contain particles of two different species 'N' and 'n'. The first box contains 'N' identical non interacting particles in a volume V. The second box contains 'n' non interacting particles. The third box is the result of mixing...
  23. K

    Automotive Can hot air replicate the sound effects of exhaust gases?

    Hey guys, is it possible to replicate the sounds produced by exhaust gases in a car by using only hot air? Thanks in advance for your responses.
  24. V

    Thermal coefficient of expansion in gases

    I know that the variation in a gas' volume is equal to ΔV = γ⋅V[initial]⋅ΔΘ with ΔΘ the variation in temperature and γ=1/237 the thermal coefficient of expansion in gases. Could someone please explain to me why γ=1/237 please ? Thanks a lot, V
  25. B

    I Why triatomic gases have internal energy 7RT/2 ?

    This table is given in my book, $$\begin{array}[c!c!c!c!] \text{ }&\text{ Transitional }&\text{ Rotational }& \text{ Vibrational} \\ \hline \text{Linear molecules} & 3&2& 3N -5\\ \hline \text{Non-Linear molecules} & 3&3& 3N -6\\ \hline \end{array}$$ It is also given...
  26. V

    A doubt from Kinetic Theory of Gases

    I have read Average translation kinetic energy is 1/2RT per degree of freedom and Average translation kinetic energy for an ideal gases is 3/2RT.How? Does it imply f=3 for all ideal gases?
  27. T

    (2/3) as constant factor In Kinetic theory of gases

    Hi I'm in high school but what I'm going to ask you is probably being teached in college. General formula: p=(2/3)*(N/V)*Ek p- pressure N- amount of molecules V- volume of the container Ek - AVERAGE kinetic energy I've been told by my physics teacher, that 2/3 constant factor in kinetic theory...
  28. Ravi Singh choudhary

    Pressure should decrease in zero gravity?

    Pressure can exist in a container of gas even if there is no gravity. From kinetic theory of gases it is assumed that pressure exists due to momentum transfer between molecules and the wall. Suppose I have a closed container on Earth at sea level filled with air. Now I carried it to zero gravity...
  29. A

    Two monatomic ideal gases are in thermal equilibrium with ea

    Homework Statement Two monatomic ideal gases are in thermal equilibrium with each other. Gas A is composed of molecules with mass m while gas B is composed of molecules with mass 4m. The ratio of the average translational kinetic energies KA/KB is: Homework Equations KE=0.5xmxVavarage^2...
  30. A

    Thermodynamics -- mono and diatomic gases

    Homework Statement The 4 processes involve one mole of either mono- or di-atomic gas with the same amount of heat (absorbed or discharged) •Which belong to the mono and which to the diatomic gas? Homework Equations i don't know which equations I should use and how start solving it.. I...
  31. A

    Thermochemistry & Gases in Electrical Engineering?

    I'm a first year electrical engineering student and in my General Chemistry class, every other week, we're required to write a paragraph about how each weeks material relates to your future career. As I am in electrical engineering, I don't see much relation to any topic. This week is...
  32. B

    A See gases with consumer IR camera

    I am trying to do a project to simulate MODIS (NASAS' telescope addon). I have a flir one which helps me replicate the thermal camera but i need also a CO2 camera. I know its possible with a ir camera with a 4um filter but my camera apparently works from de 8-15um range which is out. I though...
  33. Allen_Wolf

    Gases & Trees: Carbon Dioxide & Oxygen Usage

    1)How much carbon dioxide does a mature tree use everyday? 2)How much oxygen is used by a mature tree everyday?
  34. R

    I Why equal volumes of diferent gases have the same number of molecules @ STP?

    Hi, A silly techiniacal, very basic but logical question. Trying to understand since long but unable to justify myself. Can u help? Deferent gases have deferent molecular size, then how is it possible that equal volume of deferent gases have same numbers of volume at standard temperature &...
  35. Jehannum

    Velocity of gases in a flue / stack

    I know the flow rate of gas (products of combustion + air) entering a natural draught (no fans) flue. If the flue is removing all the gas: velocity of flue gas = flow rate (corrected for thermal expansion) / flue csa As the flue gas moves up the flue what happens to its velocity? In...
  36. F

    Why don't gases settle on the ground due to their weight?

    In studying physics over many years, I am still perplexed that gases have weight. I understand that gases are composed of molecules, but if they are moving in all directions with much space between each molecule, how is there a downward weight that can be measured with all that space in between...
  37. M

    Thermodynamics Gases: Final Temp, Work, Internal Energy, Q

    Homework Statement two cubic ft, of air at 85 f and 13.9 psi, compress to 115 psi. What is the final temp, the work, the internal energy "delta u", and Q Homework Equations well i don't have any equations, i am asking for the equations The Attempt at a Solution i don't know how to approach to...
  38. C

    Thermodynamics - Two gases in a container

    Homework Statement Two kilograms of air at 5 bar, 350 K, and 5 kg of carbon monoxide, initially at 4 bar, 450 K, are confined to opposite sides of a rigid, well-insulated container by a partition. The partition is free to move and allows conduction from one gas to the other without energy...
  39. Dakota

    Can all gases be ionized to make a plasma?

    I sort of new to the states of matter, so please use English (explain what all the big words mean). First of all what does ionizing even mean? second every type of matter of 4 states?
  40. C

    B Can all elements, (not including gases) form Ionic Bonds?

    I've been looking all over the internet, can calcium and iron form an ionic bond, Gold and Radium, Sodium and Tin. If those elements happened to run into each other. Also, another thing I don't understand is why don't the atoms in my hand bond with atoms on the wall when they come into contact.
  41. M

    I Ideal Gases: O2 & H2 - Kinetic Energy Comparison

    Hello, I want to make sure I understand the following considering ideal gases. Assuming I have two different types of gases, say, O2 and H2 (each at thermal equilibrium), is it correct to say that the kinetic energy of the O2 gas equals to the kinetic energy of the H2 gas since they're both...
  42. E

    Gases that absorb IR radiation

    Hello, I'm looking for a gas (hopefully one that is readily available) that will absorb Nd:YAG laser radiation at 1064 nm. The purpose is to heat the gas to transmit heat into a glass fiber composite which normally does not absorb IR light.
  43. M

    Find Heat Energy Needed to Expand Gas to Triple Volume

    Homework Statement When 0.40 mol of oxygen(O2) gas is heated at constant pressure starting at 0 degrees C, how much energy must be added to the gas as heat to triple its volume? (The molecules rotate but do not oscillate) Homework Equations pV=nRT p1V1/T1=p2V2/T2 Q=mcdT Value of Cp for Oxygen...
  44. kini.Amith

    Classical A source for solved problems in Kinetic theory of gases

    I am doing a course on statistical mechanics and we are using the textbook by Mehran Kardar. We are currently dealing with a chapter on kinetic theory. The problem is, I find the exercise problems to be quite tough (and many of my classmates agree with me), and there are no good solved examples...
  45. Elena14

    Dalton's law for ideal gases at different temperatures

    How would Dalton's law be affected when there are two ideal gases in a container at different temperatures? Let the gas with higher temperature be gas A and the gas with lower temperature be gas B. Then heat will be transferred from gas A to gas B due to which kinetic energy of the molecules of...
  46. D

    What Is the Correct Theoretical Yield of HNO3 in This Chemistry Problem?

    Homework Statement Hello! I would be grateful for your help on finding my mistake - somehow my answers are wrong compared to the answer from the book. Here is the exercise from a paragraph on gases (cumulative gas law, basics): Consider the reaction for the synthesis of nitric acid: 3NO2 + H2O...
  47. M

    Calc Vol of 1 Mol Steam @ 100°C, 1 atm: Ideal Gas Eqn

    Homework Statement Calculate the volume of 1 mol of steam at 100°C and a pressure of 1 atm assuming that it is an ideal gas. Homework Equations PV=nRT The Attempt at a Solution Well, if I am honest I was just going to re arrange the above equation for V and plug the numbers in but that seems...
  48. O

    Helmholtz potential for mixture of simple ideal gases

    Homework Statement Two subsystems within a 20 l cylinder are separated by an internal piston. Each of them is initially composed of 1 mole of component 1 and one mole of component 2, both of which will be treated as a monatomic ideal gas. The cylinder has diathermal walls and is in contact...
  49. R

    Rate of Gaseous Diffusion into a Vacuum

    Hello Everyone, I have a question regarding the diffusion of a gas (or mixture of gases) into an evacuated space. The situation I am picturing is one where you have two vessels of equal volume, one contains a gas at room temperature, some known pressure (say ~760torr), and the other at static...
  50. J

    Potential energy in solids,liquids and gases

    Homework Statement Is the potential energy between atoms in solids, liquids and gases, elastic or electrical? I've read in some sources that for solids, p.e. > k.e. because it has the strongest intermolecular forces among the three states of matter. So I'm assuming it is elastic potential...
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