# 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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### If liquid and gas are both chaotic states of matter, what's the difference between them on the molecular level?

I'm a laywoman in physics and recently found myself pondering about the matter reflected in the title of this post. To make my question more precise from the mathematical standpoint, let's suppose ...
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### Do gases become more opaque as they are cooled or compressed?

So recently I was thinking gases (at least colourless ones) are more transparent in their gaseous state than liquid state. And as we talk of continuity in liquid and gaseous state (fluids) is it ...
29 views

### Calculate the compressibility coefficient $k$ using the van der Waals equation [closed]

I have that van der waals equation $$\left(P+\frac{a}{\bar{v}^2}\right)(\bar{v})=RT$$ Where $P:$ is absolute pressure of gas, $kPa$ $T:$ is temperature, $K$ $\bar{v}$: is the molar volume of ...
12 views

### Determine gas parameters from vapor pressure information [closed]

Given the empirically derived vapor pressure curve for a given material, what gas properties (compressibility, ratio of specific heats, viscosity, etc.) can be defined as a result over the range for ...
13 views

### Is there a list of the change in specific volume of substances when they change phase from liquid to gas at atmospheric pressure? [closed]

The volume of water changes when it changes to steam. In which compound is the change highest?
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### Mixing 2 gas flows of different pressure to get flow rate fraction [closed]

If you have two gasses constantly supplied at different pressures into a mixing chamber, how can you solve for the ratio of the two gas flows (don’t care about the values of the flow rate) and the ...
27 views

### Why does breakdown voltage increase with pressure in gas insulators

There are two main theories which I have been reading into Townsends avalanche effect and Paschen's curve. I understand that as electrons move from negative to positive electrode they collide with gas ...
46 views

### Two versions of Diffusion coefficient

I found two versions of the Diffusion coefficient, first: $$D=\frac{\pi \lambda }{8}\overline{c}$$ Where $\overline{c}$ ist the particles mean thermal velocity and $\lambda$ the particles mean free ...
69 views

### Linear or quadratic damping term in Euler's equation?

In the Euler equation with frictional damping $$\begin{cases} \rho_t + (\rho u)_x = 0 \\ (\rho u)_t + (\rho u^2 + P(\rho))_x = \color{red}{-\alpha \rho u} \end{cases}$$ sometimes I see a different ...
77 views

### Time period of piston performing SHM

Suppose I have a closed piston-cylinder system which contains an ideal gas,and it is being compressed adiabatically by the piston which has a vertical orientation,and in doing so,the piston is ...
25 views

### Thermodynamics: work done on a gas

How much work would be done on a gas contained in a metallic container at high pressure if it is leaked slowly into the atmosphere?
29 views

### Is static electricity an “electrical discharge”?

I understand that any electrical discharge such as corona discharge is the scattering of electrical charge through a medium; most likely a gas ("discharging charges"). As the air is a gas, would it ...
43 views

### Time between collisions and collision time

I’m having a hard time really getting how the relationship between pressure and square mean velocity of a gas is derived for one single reason...seems like I don’t really know what impulse is. From ...
36 views

### Finding entropy of Nitrogen at low pressures

I'm trying to calculate the entropy of gaseous Nitrogen (assumed to be ideal) at a particular state in a thermodynamic cycle. I know the pressure, temperature, and specific volume, but all property ...
32 views

### Bifurcation of Van Der Waal equation for real gases

Van Der Waal's equation leads to a cubic equation in v of the form $$Pv^3-(bP+RT)v^2+av-ab=0$$ This equation has 3 roots for $T<T_C$ and one root for $T>T_C$ I understand why region ABCDE is ...
35 views

### Would connecting two pressurized gas tanks together exchange gases?

While the answer to the title is inevitably "Yes", allow me to clarify. I have no background in physics, so please bare with me and I'll be happy to add any clarifications requested in the comments. ...
27 views

### Pressure on wall by gas molecules

Pressure by gas molecules of an ideal gas on the walls is P = nRT/V But by derivations P=1/3 nmv², where v is velocity. Are they equal, if yes, then it means that we can deduce volume of free path ...
171 views

### What is the air pressure on a magic wall that reflects all incident molecules perpendicularly to itself?

I am a total laywoman in physics and humbly hope that physics experts of this SE can help me find the answer tо my question. A friend of mine and I had an argument about that question, and I am very ...
28 views

### What pressure should be used when calculating Work in gas expansion?

The formula for the work done by a gas is $W = \int_i^f P dV$. What pressure should be used here? I'm asking because I thought you use the gas pressure at every instant of an expansion. For an ideal ...
40 views

### In the evaporation process, will the temperature of both liquid and vapor molecules decrease?

The theory says that the molecules that become vapor "take" some energy from the surrounding molecules (the latent heat of evaporation). As a consequence, the temperature of the liquid falls a bit. I'...
38 views

### Is there a difference between two molecules, of the same substance, one in liquid phase and the other in gaseous phase?

What are the main differences? Volume, shape, or what?
1k views

### Why are sound waves longitudinal even though they are mechanical energy?

Waves on a string, ripples on a pond are transverse waves generated by mechanical energy and in the simplest form oscillations. Sound also is a form of energy and basically oscillations. What makes ...
61 views

### What causes vortices at the billiard ball particle level?

In a fluid/gas model consisting of billiard ball hard particle collisions what are the key behaviours that are needed to manifest the larger scale vortices? I can only seem to find descriptions of ...
31 views

### How does water vapour replace air molecules?

I know that density of moist air is less than density of dry air becuase water molecules replace air molecules, and hence as the average molecular mass of water is less than that of air, the density ...
55 views

### Operation Of A Constant Volume Gas Thermometer

Concerning the mechanism of a constant volume gas thermometer, I was wondering how the adjustment of the second tube upon the open side increases the pressure. I know how the gas placed in the ...
77 views

### Can metal or carbon vapour conduct electricity?

Not a duplicate of Can Gases conduct Electricity, since it asks about ionised gases, which is irrelevant to my question. This is what I already know: All metals have a giant metal lattice, where ...
15 views

### Choosing Molecular Beam Carrier Gas

What is the specific criteria for picking the carrier gas for a molecular beam? If you are studying a large neutral species, does it make sense to choose argon over helium for better collisional ...
31 views

### Perfect gas relationship between pressure and density

I've been given the following equation for a perfect gas: \begin{equation} p = k \rho^\gamma \end{equation} Where $k$ and $\gamma$ are constants. I'm trying to find out where this comes from or a ...
55 views

### What will happen if you fired a gun in a room filled with hydrogen gas? [closed]

Will the room explode? How does it happen?
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### If water vapor changes its phase, how is it possible to maintain specific volume?

I was doing my thermal engineering exercises when I encountered a problem. The problem specified a fixed and rigid container with a volume $V=0.17\ m^3$, as I have a $T-S$ diagram for water, they give ...
21 views

### Exchange energy per electron in uniform electron gas

All day, I have been trying to get the correct expression for the exchange energy per electron of a uniform electron gas. All references agree on the units (Hartree units) and the following notation:...
2k views

### Would a helium-filled football/soccer ball actually fly farther than a normal ball?

Armchair physicist with a rudimentary understanding of physics here. I was watching a video today that tested the effects of a football filled with normal air, helium, and sulfur hexafluoride. ...
50 views

### What would be the distances between compressors part of a gas pipeline from Earth to the Moon?

This paper, acquired from this question about tethers on the Moon, describes LADDER, a mission to deploy a Lunar Space Elevator [LSE]. The space tether, made of Zylon fiber, would be 264,000 km long, ...
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### In a pressurized container of sufficient size, would there be a pressure gradient due to gravity?

If you have a pressurized container of sufficient size, would there be a pressure gradient due to gravity? Pascal's law indicates the pressure is the same everywhere in the container. Let's ...
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### Finding the flow rate of a gaseous oxidizer flowing through a solid fuel (and they're combusting!)

I'm wondering, is there a way to calculate the volumetric flow rate or mass flow rate of oxygen flowing through a solid fuel (ex. paraffin wax) and combusting with it? After the combustion, the flow ...
27 views

### Typical balloon volume-pressure law

I need to find the gas pressure required to make a balloon take a given volume, knowing the gas densities and atmospheric pressure. Is there a typical law/correlation that can be used to approximate ...
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### Shouldn't Z(compressibility factor) be < 1 for all real gases?

So compressibility factor(z) is defined as $$Z = \frac{V_{real}}{V_{ideal}}$$ where $V_{real}$ is volume occupied by real gas and $V_{ideal}$ is volume occupied by ideal gas at same conditions but by ...
73 views

### Which explodes first? Vacuumed tank or pressurized tank?

We have been arguing with a friend and couldn't agree. Here is the question: We have two systems. In both of the systems, we have an identical sphere tank. In the first system, we are vacuuming the ...
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### Will a can filled with vacuum move when we let in air? [duplicate]

This picture is from L.C.Epstein's book Thinking Physics. The upper can is filled with compressed air, and, when an opening is made on the right, the air comes out and the can shoots left. The ...
69 views

### How do you define volume for gases? [closed]

Straight forward question. If atoms forming a gas float far from each other, how can we assign a volume to it? if it is in a container, perhaps we'd say the atoms, or molecules, reach every corner and ...
10k views

### Gas pipes - why does gas burn “outwards?”

I've often wondered if a gas cylinder is connected to a hob (say, or a boiler or whatever) and someone turns the knob to allow gas to flow, why is that when a flame is held to light the gas it isn't ...