# 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. ### 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}...
2. ### Simulation of a gas in 2-D using a Verlet algorithm

Verlet Algorithm with periodic conditions
3. ### 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...
4. ### 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?

6. ### 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...

8. ### 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...
9. ### 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...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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!
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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...

21. ### Work done to compress gas

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!
22. ### 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!
23. ### 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...
24. ### 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...
25. ### 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...
26. ### 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...
27. ### 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...
28. ### 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...

47. ### About the binding of O2 to Hemoglobin molecules

Hello, I just learned about the binding capacity of Hemoglobin (Hb) and that it is proportional to the partial pressure of O2 in the blood here is the curve : it does have a sigmoidal shape, but here is the problem: in the lecture, it's said that Hb has an increasing affinity to O2 the more...
48. ### How to find velocity of gas pump flowing into car tank

The general balance equation is as follow: d[m{u+gz+v2/2)sys=(u+gz+v2/2)dmin-(u+gz+v2/2)dmout +dq+dw. I understand that I would take in consideration the cross sectional area as well as the mass flow rate. However I can't figure out what else to consider as if atm pressure should be considered...
49. ### Calculating Velocity & Field Strength of Gas: Help Needed!

For the first calculation of the velocity of the gas I use the first equation and this converted in meter would be look like this (first value as an example) v=299792458 m/s * (6.76813x10^-7-6.768x10^-7)/6.768x10^-7 =5836.03m/s or 0.0019c this was the velocity of the gas for the first spectral...
50. ### Cleaning of the finned tubes on gas cooler without disassembling

Hi, I've been thinking about the solution for cleaning a water-cooled gas cooler and would love to hear some advice from the smarter people with more experience. Description - I will try to roughly explain the concept. Gas Cooler is used to decrease exhaust gas temperature. The exhaust gas...