Questions tagged [gas]

This tag is for questions relating to "gas", one of the four fundamental states of matter (the others being solid, liquid, and plasma). Gases follow certain laws known as the gas laws. These laws tell us about the behavior of gases i.e., the values and relations of temperature, pressure and volume etc.

Filter by
Sorted by
Tagged with
0
votes
0answers
23 views

Gas pressure along the axis in effusion

I'm trying to approximate the pressure P along the axis x, i.e. P(x), for the following setup. At one end of a cylinder a gas is inserted (at some pressure, let's call it P0). At the other end of the ...
1
vote
1answer
36 views

Why smoke particles go down? [closed]

Let's say in an apartment the upstairs neighbor smokes but the smoke goes down to the below neighbors. Is it a difference in temperature that causes the smoke to flow down instead of going up through ...
0
votes
0answers
22 views

How to calculate the velocity of an ionised gas when a field of 100 Tesla is applied?

Say I have an ionised gas, oxygen/hydrogen and I am creating a magnetic field with a strength of 100 Tesla by inducing a voltage of 100 V/S in a magnetic material (the charge becoming 100, this gas is ...
0
votes
1answer
14 views

Quantifying how fast gases reach equilibrium again when opening a window

When opening a window in a typical room with higher CO2 and lower O2 concentrations compared to the outside, how fast does it equilibrate again? Assuming no wind, just diffusion, the answer still ...
1
vote
2answers
64 views

If the earth constantly exerts a force on air molecules downwards, then why do they not fall to the ground?

I'm sorry if this seems like a really stupid question but it has really puzzled me... The earth exerts gravitational force on all objects with mass, and gas has mass. I know that this force results in ...
0
votes
1answer
16 views

Derivation of pressure of a gas from mean sqaured speed of molecules

I understand that the pressure exerted by a molecule on the walls of a container, in the $x$ direction is given by $P=n m v_x^2$ Where $v_x$ is the mean $x$ component of velocity, $m$ is mass and $n$ ...
0
votes
1answer
36 views

In kinetic theory of gases, how do we figure out the forces exerted by walls on molecules?

This is a cube with each side having a length of $l$ containing a certain amount of molecules in it. Let's say a molecule of mass m is traveling in the $y$-direction with the velocity $v$ and hits the ...
1
vote
2answers
108 views

Why does gas not do work when expanding in a vacuum?

Why does a gas do no work when expanding in a vacuum? I know it is true that there is no opposing force from other air molecules for the gas to overcome in a vacuum, so that gas molecules won't do ...
0
votes
1answer
28 views

A strange consequence of Isotropy in Phase Space

In Goodstein, States of Matter, page 66 the following is stated: For a single particle the number of states in a region $d^3pd^3r$ of its phase space is: $$\frac{d^3pd^3r}{(2 \pi \hbar)^2} \tag{1.3....
0
votes
0answers
25 views

Fixed volume air flow to vacuum

I have a work project and am trying to wrap my head around the foundational aspects of the fluid dynamics before I attempt to take measurements. I want to have an idea of what to expect compared with ...
0
votes
0answers
26 views

Thermal velocity vs speed of sound

Is it possible that for a gas, speed of sound$>$thermal velocity? I cannot imagine it since, for the ideal gas limit, the interactions solely rely on the bouncing back of molecules
1
vote
1answer
23 views

Vapor pressure in a closed box

If there is a closed box at room temperature with water inside after a certain point there will be an equilibrium condition where some water is liquid and some is vapor. So there will be a certain ...
2
votes
2answers
73 views

What is this atmospheric escape chart actually showing?

The wikipedia article on atmospheric escape has this chart: It all seems plausible enough... for a body to retain an atmosphere of a gas, the velocity of gas molecules in its exosphere must be mostly ...
7
votes
3answers
777 views

Why are spectrums of incandescent light bulbs continuous despite the presence of Argon around them?

Incandescent bulbs emit light by heating a filament using electricity, this would lead to a continuous spectrum according to Kirchoff's first law. However, the glass casing around the filament is ...
0
votes
0answers
16 views

Steam in boiler from evaporation not boiling

Vapor pressure inside a closed container keeps building up and the boiling point of water become higher. What if the steam is required to reach say , 30psi, and the pressure in the boiler is that ...
4
votes
2answers
68 views

Does a gas move from a region of high to low pressure according to it's own partial pressure rather than the total gas pressure?

I have a plastic bottle that is impermeable to ${\rm CO}_2$ but slightly permeable to $\rm O_2$. If I fill up the bottle with pure $\rm CO_2$ at $3$ atmospheres and expose it to $\rm O_2$ at $1$ ...
0
votes
0answers
31 views

What is the justification for the theoretical value of the adiabatic index of $\rm CO_2$ of 1.30 at room temperature?

I'm currently investigating an experiment to determine the adiabatic index of helium, nitrogen and carbon dioxide at room temperature and am attempting to come up with / justify theoretical values of ...
0
votes
0answers
16 views

Does viscosity arise from the increase in intertia created by the movement of molecules?

Cohesion is how strongly a substance holds itself together, and viscosity has been described as the substance's internal friction. Viscosity has mostly been explained to me via allusions to substances ...
0
votes
0answers
20 views

What is the output pressure graph in my simple Pneumatic system?

I am doing basics Pneumatics and I have a question about how one would calculate the following. In general I hope to get an idea of how to dimension Pneumatic systems. I have done differential ...
48
votes
7answers
7k views

Why does carbon dioxide not sink in air if other dense gases do?

Why does carbon dioxide not sink in air if other dense gases do? We evidently do not suffocate by carbon dioxide sinking to the bottom of the atmosphere and displacing oxygen and yet there are gases ...
1
vote
2answers
85 views

In plasma when we introduce a positive test charge then electron cloud shield it, why don't they stick to it and neutralise it?

When a positive test charge is introduced into a plasma, then there is a formation of an electron cloud which shields it. Why don't these electron stick to the positive charge and just neutralise it? ...
2
votes
3answers
72 views

Why is the slope of pressure and volume almost zero below critical point for liquefaction of gas?

Image shows the Andrews isotherms regarding liquefaction of gases. Why is the $PV$ curve almost horizontal from point $B$ to $C$? I want to understand why does a small increment in pressure result in ...
1
vote
2answers
307 views

What is quasineutral in plasma physics?

What is quasineutral gas? In plasma physics, what exactly quasineutral means? In definition of plasma, it is written that plasma is a quasineutral gas of charged and neutral particles which exhibit ...
5
votes
4answers
389 views

Is it theoretically possible to keep the volume and temperature of a gas undergoing a chemical reaction, to which heat has been supplied, constant?

I was reading about enthalpy$^*$ when I thought that if it is possible for the gases undergoing a reaction to be supplied heat while keeping the pressure and temperature constant and just allowing it'...
-2
votes
1answer
58 views

Why do electrons or other plasma species follow Maxwell-Boltzmann distribution in plasma?

In plasma physics why do electrons and other plasma species follow maxwell boltzmann distribution? Is there any physical reason behind it or simply becoz most plasmas follow classical physics.
1
vote
1answer
49 views

Hit rate of molecules on a wall

Reviewing my final from last semester to prep for comps: Question: A piston of mass M can move freely in a tube with cross-section area A filled with ideal monoatomic gas with molecular mass m ≪ M and ...
0
votes
1answer
62 views

The internal energy of a real gas

I apologise in advance, but I am asking for clarification. I learnt from a first year undergraduate physics book that in the case of ideal monatomic gases, the internal energy is given by $E_{int} = n ...
0
votes
2answers
209 views

Free Expansion - Isothermal vs Adiabatic

By free expansion, I am referring to gas kept in a piston-cylinder arrangement freely allowed to expand against vacuum. It is clear to me that free expansion is an irreversible process because if it ...
0
votes
0answers
21 views

Volume correction of Van der Waal's equation

A simple derivation of the ideal gas law by assuming all gas molecules to be perfect spheres is as follows: Considering some area of the wall of a container A, the pressure exerted by all molecules ...
2
votes
2answers
94 views

How is the Pressure defined in the Van der Waals' equation?

I have some doubts regarding the Van der Waals' equation which relates the Pressure, volume and temperature of real gases. It is given by : $$(P_{real}+\frac{an^2}{V^2})(V-nb) = nRT$$ I also read that ...
0
votes
1answer
29 views

Form of Energy in Compressed Gas

What would be the best way to categorize the energy stored in a compressed gas? Should I call elastic potential energy? Maybe mechanical? It's not that exotic a way to store energy but it doesn't ...
-1
votes
1answer
25 views

Why do lighter gases float?

Why do lighter gases float? What makes them float? Is there a force pushing them upward or are they less affected by gravity.
0
votes
4answers
51 views

Why is there atmospheric pressure?

Why is there atmospheric pressure? Gas molecules have empty spaces between them right (intermolecular space). But to have atmospheric pressure all the gas pressure will have to line up without any ...
0
votes
1answer
42 views

How to simulate mixing of gases with different compositions?

Let's assume that we have the following apparatus in which volumes A and B are separated by a magical, impermeable, adiabatic barrier labelled S. (Let's also assume that the volumes are cubes, and ...
0
votes
1answer
52 views

Explaining $\beta_p$ curve for Van der waals gas

Given the Van der waals gas $$\left(p+\frac{a}{V^2}\right)\left(V-b\right)=RT$$ in standard notations. I tried finding isobaric expansivity $\beta_p$ which is defined as $$\beta_p\equiv\frac{1}{V}\...
1
vote
2answers
48 views

How to dilute 5000 ppmvol of $\mathrm{CO}_2$ to obtain 250 ppm with a fluxmeter?

My problem is that I have a tank, containing $\mathrm{CO}_2$ at 5000 ppmvol, Oxygen $21\%$ vol and Nitrogen the rest, connected with a mass flow controller (flux max at $150$ ml/min). And I have a ...
1
vote
1answer
111 views

How does the kinetic-molecular theory explain why atmospheric pressure is greater at lower altitudes than at higher altitudes?

It is believed that pressure exerted by a gas is caused by "momentum exchanges by colliding molecules". Also it is a fact that the atmospheric pressure on a body is greater at lower ...
0
votes
0answers
16 views

How much pressure does it take to start an underwater gas fire?

It's recommended for underwater use of acetylene torches that you set the oxygen pressure to 90 psi, so that it creates an air bubble which allows the fire to get started. This made me wonder... do ...
0
votes
1answer
20 views

Could you survive on hydrox in at 10 atmospheres?

I was told that hydrox is incredibly dangerous, that pure oxygen will combust without any source of ignition at 3 to 4 atmospheres of pressure, and that because humans are hydrocarbons they will act ...
0
votes
1answer
42 views

The effect of hand fans for better breathing in emergencies

Suppose I am in a room or system with a lot of smoke and it is difficult to breathe. If I put a hand fan in front of my face, does the wind from the fan blow the smoke away from my face, making it a ...
0
votes
2answers
582 views

How many Degrees of Freedom do Linear Triatomic Gas Molecules Have and Why?

I read this in one of my textbooks that stated Linear Triatomic Gas Molecules like CO2, HCN, CS2 in which all the atoms are linear, the total number of degrees of freedom are Nf = NT + NR + NV where ...
1
vote
2answers
849 views

A simple way to make liquid oxygen at home

I have an idea to make liquid oxygen at home, but without any calculations, I am not sure whether it will work at all. The idea is based on the fact that gases tend to liquefy easily in higher ...
1
vote
1answer
36 views

Thermodynamics - Superheated vapor expanding into vacuum

When I have a gas in one vessel which is expanding into another vessel in vacuum, I know the work done will be $0$. My question is, what if that gas is not ideal, and it's a superheated vapor, is ...
0
votes
1answer
9 views

Diffusing pressurized gas with minimum noise

Problem: I need to diffuse pressurized dry air (about 4-6 bar) in to a room, while creating minimal noise. The inner diameter of the tube is about 8 mm. Without a proper nozzle, there are bond to be ...
0
votes
0answers
66 views

Air's considerable resistance to compression

My conception of air has been that, as a gas, its molecules are loosely situated. When placing food items in a plastic, sealable storage bag, to avoid a major air pocket one has to squeeze much of the ...
1
vote
1answer
82 views

Definition of $PV$ work

A balloon contains gas with pressure $P_1$, volume $V_1$. It is connected to a container with vacuum with volume $V_2$, and the gas is released into the vacuum. What is the work done by the gas and ...
1
vote
0answers
12 views

What is the most common method used to cool hydrogen below its boiling point?

I would like to know what methods companies/organizations/scientists use to cool gaseous hydrogen below its boiling point of ~250 degrees Celsius. I am a new student to thermochemistry and am not ...
0
votes
3answers
87 views

Why are there two states of matter in a bottle of gas?

Say a bottle of natural gas used for heating or cooking. There is a liquid phase, which I believe is the densest part, at the bottom of the bottle. And on top of it, there is presumably gas in a ...
0
votes
1answer
27 views

Does electric current through gases emit light?

Not electric spark or electric arc, just normal current through gases created by heating the air between cathode and anode as shown in the following video at 1:25. https://www.youtube.com/watch?v=pg0-...
0
votes
2answers
71 views

Why liquids evaporate completely when heated at their boiling points?

I'm confused about why the boiling of liquids happen. The boiling point of a liquid is defined as the temperature in which it's vapor pressure is equal to the pressure of the gas above the liquid( for ...

1
2
3 4 5
11