# 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.

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### 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 ...
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### 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 ...
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 ...
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### 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 ...
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 ...
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### 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 $n$ ...
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 ...
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 ...
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### 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 ...
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 ...
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 ...
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### 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 ...
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### 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 ...
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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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 ...
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### 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 ...
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### 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 ...