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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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Isentropic or isenthalpic expansion for the remaining fluid in a previously pressurised tank? [closed]

Imagine a container filled with ammonia at 25 bar and 100 degC. Assume that an orifice is opened, so that fluid can flow through ...
Felix's user avatar
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2 answers
93 views

Why don't disturbances/wind move at the speed of sound in air?

Why don't sound waves move at the same speed as air that has a pressure differential? Imagine you have a box that is filled with air. One half high pressure air, the other half low pressure. They are ...
Wyatt's user avatar
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1 answer
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Why should the rate of evaporation of liquids depend upon the rate at which the molecules strike the surface?

This paper says: The development of the kinetic theory of gases led to the conclusion that the maximum rate at a particular temperature would be given by the rate at which molecules strike the ...
Ritesh Singh's user avatar
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2 votes
2 answers
58 views

If air was the same density as water, but still a gas, could you swim in it?

I'm not talking about normal physics here, as it would be extremely hard to get such a situation to arise, this is more a hypothetical question. If air was the same density as water, while still ...
Lux's user avatar
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2 votes
0 answers
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Were radioactive materials used in neon indicator lamps? [closed]

Were radioactive materials used in neon indicator lamps? Old-fashioned glow starters for fluorescent lighting [How a glowstarter works] often contain small traces of radioactive gas (like $^{85}$Kr or ...
Jos Bergervoet's user avatar
-1 votes
0 answers
17 views

How to calculate the evaporator and condenser pressure in a vapour compression refrigeration cycle?

Imagine a basic vapour compression refrigeration cycle. A compressor which sucks gas from the evaporator and pumps it into the condenser at high pressure. The gas loses heat and becomes liquid in the ...
sms_sr's user avatar
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8 votes
3 answers
2k views

How does gravity overpower a vacuum?

While watching experiments with vacuum chambers, I had a thought. If you put a sealed box at normal atmospheric pressure inside a vacuum chamber, pumped out the air and pierced the pressurized box I'd ...
Walt Spring's user avatar
4 votes
2 answers
139 views

Why can photon be treated like gas?

In Cosmology, especially when studying Cosmic Dynamic, sometime we will treat photons as gas to calculate its pressure, but according to my understanding, photon and gas are nothing alike. Why can ...
Polaris5744's user avatar
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1 answer
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How does ionization of gas molecule affect the translational kinetic energy of the molecule?

Some things I understand to be true: When we raise the temperature of a gas to around 10-20,000 Kelvin, the molecules of gas start to ionize, form a plasma, according to the Saha equation. The ...
Hugh Perkins's user avatar
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36 views

Calculating partial pressures of real gases in a ternary mixture

I need some help on how to calculate the partial pressures of a ternary mixture using the Peng-Robinson equation of state (PR-EOS) instead of the ideal gas law. I need to prepare a mixture of three ...
user3212953's user avatar
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1 answer
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How do I create a highly conductive vapor cloud? [closed]

I'm working on a project that requires that I create an electrically conductive gas cloud that can conduct voltages as low as 1.5v from a regular double A battery. I've been looking into using mecury ...
TechDroid's user avatar
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Static pressure vs ambient pressure

If in a real scenario, a flat surface with a flush perpendicular closed duct of small diameter is exposed to a tangential fluid flow(laminar and naturally with the presence of boundary layer effect), ...
Sergio's user avatar
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1 answer
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Modelling the number of times a gas tank can be filled

I'm currently working on a project where I need to estimate how many times a large, high-pressure gas tank can refill a smaller tank. For this purpose, I'm using a pressure regulator to manage the ...
Enzo 's user avatar
3 votes
1 answer
308 views

Ideal Gas law and Universal gravitational constant

In a hypothetical universe with a different Universal gravitational constant $G$, will the nature of ideal gas change by any means? i.e, will $PV = nRT$ be no longer applicable in that case?
Teflon's user avatar
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Excluded volume in van der Waals' Equation

As per my understanding, excluded volume is defined as the volume excluded to the rest of the gas molecule's centers because of its presence. During bimolecular collisions, there is some overlap in ...
Marc Carlsan's user avatar
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1 answer
36 views

Force and massa unit [closed]

why in this question did the question answer only perform the product between area*P to calculate the mass? Question: Answer: Shouldn't the mass be calculated as $m = (P \times A)/g$? Considering ...
Everson Gomes's user avatar
1 vote
0 answers
54 views

Finding formulas for molar internal energy and molar enthalpy of mixing fluids

There is a Y-shaped pipe connection. One fluid flows through one pipe with molar flow $\nu_1$, molar internal energy $U_1$, molar enthalpy $H_1$; through the second pipe - another fluid with molar ...
Igor's user avatar
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1 answer
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How can I find the fundamental equation of the system?

A gas respects the following equations $$T=\frac 32(u+\frac 1v)$$ $$P= \frac Tv -\frac1{v^2}$$ Where $T$ is a thermodynamic temperature, $P$ is the pressure, $v$ the specific volume and $u$ the ...
Marcelo's user avatar
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3 votes
1 answer
75 views

Why is the number of microstates corresponding to a macrostate even finite for an ideal gas in a box? [duplicate]

I was looking at the Sackur-Tetrode equation which gives an exact formula for the entropy of an ideal gas. I tried to relate it to Boltzmann's famous $$S = k_B \ln(W)$$ where $S$ is the entropy and $W$...
Hadi Khan's user avatar
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1 answer
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Keeping sparkling water inside a bottle as aerated as it was before opening bottle

So when you open a new bottle of sparkling water (or soda) it's very fizzy and aerated. However, when it is stored for quite a bit (no matter how tightly you close the bottle cap) it loses some gases ...
bonbon's user avatar
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2 answers
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How it is possible to vary the pressure of a gas under constant $V$ by varying $T$ while also considering the expansion or contraction of the gas?

Is it possible to vary pressure of a given quantity of a gas without changing its volume by varying only temperature in real life? Why the varying temperature does not change the volume? Why the gas ...
Vinay5101's user avatar
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0 answers
55 views

How to calculate the specific heat jump for a van der Waals gas at a non-critical volume?

I am currently self-studying Statistical Physics by Professor Schwabl and encountered a problem in the book (problem 5.5) that has significantly challenged my understanding. The problem is brief but ...
John Title's user avatar
0 votes
2 answers
45 views

Gas and Vapour liquefaction

I am a bit confuse in the first statement. I think the statement is implying vapour as 'former' and gas as 'latter'. Am I correct here? But gas can be liqufied with pressure alone below the critical ...
Cerebral cortex 's user avatar
5 votes
2 answers
289 views

Helium in Uranus atmosphere

I read that in 1986 Voyager 2 measured the composition of Uranus' atmosphere, which turned out to be composed of $85 \%$ hydrogen and $15 \%$ helium. It's not clear to me how this relevant amount of ...
gryphys's user avatar
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1 answer
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Derivation of the state equation of a van der Waals gas. Can I invert the derivative to help me?

The state equation of a van der Waals gas is $$\left(P+\frac{a}{v^2}\right)(v-b)=RT$$ with $a,b$ and $R$ constant. Find $$\frac{\partial v}{\partial T}\bigg\rvert_P.$$ Finding $\frac{\partial v}{\...
Marcelo's user avatar
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0 votes
2 answers
136 views

What is the equation for the speed of a molecule at a specific temperature?

What is the equation for the speed of a molecule at a specific temperature? I saw two equations $v = \sqrt{\frac{3 k T}{m}}$ and $v =\sqrt{\frac{3RT}{m}}$. What is the difference?
Arjun Raj's user avatar
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1 vote
1 answer
54 views

Why $∆U=Q_v$ only at isochoric condition for real gas?

U is a state function.So, ∆U should be same if we carry out an isochoric process from state A to State B or through any other process for real gas. And as ∆U=Qv for real gas in isochoric process, so,∆...
Parth Sahayata's user avatar
2 votes
3 answers
87 views

Different types of pressure and their sources

I’m an engineering student. So far, I’ve learned about 3 types of pressure: Static fluid pressure ($P=\frac{F}{A}$). This wouldn't exist without gravity. I’ve solved problems related to the force ...
Rikas's user avatar
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0 votes
1 answer
60 views

The mean kinetic energy of a gas particle

I'm in undergraduate stat mech/thermo. In the context of the Maxwell-Boltzmann distribution, the mean kinetic energy of a gas particle is $\langle KE \rangle = \frac{1}{2}m \langle v^2 \rangle$. I do ...
GMoss's user avatar
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0 answers
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Apparent paradox: Mass flow rate decreases when I increase nozzle diameter

I do computational fluid dynamics for a living. I have recently been working on a case in which I simulate the flow (assumed 2D) of a compressible gas from a large chamber at pressure $P_1$, through a ...
K.defaoite's user avatar
1 vote
0 answers
34 views

How to calculate the flow of air that leaks out of a container?

I cannot grasp what should be a simple gas problem (last time I worked with gas formulas was 40 years ago). Values I provide here are just for the sake of explanation. There is a thermically isolated ...
Alex Poca's user avatar
  • 111
0 votes
1 answer
40 views

How do I convert weight of compressed, liquid $\rm CO_2$ in canister to cubic meters at atmospheric pressure?

I need compressed $\rm CO_2$ for a project I'm working on, and am trying to figure out how much volume of gaseous $\rm CO_2$ I get from a given weight of liquid $\rm CO_2$ in canister. As far as I can ...
rolias4031's user avatar
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0 answers
39 views

Clarification regarding 'Boyle's Temperature' definition

In the Boyles law def- "The temperature at which a real gas obeys ideal gas law over an appreciable range of pressure is called Boyle temperature." Why "over an appreciable range of ...
SHINU_MADE's user avatar
0 votes
1 answer
164 views

Find heat capacity of Van der Waals gas

Can anyone guide me how can I find $C_P$ and $C_V$ ? There are two equations in Heat and Thermodynamics: An Intermediate Textbook Textbook by Mark Zemansky and Richard Dittman, which I think can help ...
seymatinsar's user avatar
1 vote
2 answers
155 views

A question based on the kinetic theory of gases

An insulated container containing monoatomic gas of mass $m$ is moving with a velocity $v$. If the container is suddenly stopped find the change in the temperature of the gas. I want to know why ...
NAITIK VERMA's user avatar
1 vote
1 answer
73 views

Is this a simple proof that gas pressure is a relativistic invariant?

This is a simple thought experiment that hopefully demonstrates that gas pressure is an invariant in relativity. Consider two very long sealed rectangular boxes that contain equal gas pressure when at ...
KDP's user avatar
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2 votes
0 answers
45 views

Is it possible to make a dual-mode, multi-band laser?

Understanding how N2 and CO2 gas lasers work, Is it possible to make a gas laser (i.e. with the right gas mix and excitation source) that: has more than one mode of operation, emits light in more ...
Hunting.Targ's user avatar
2 votes
0 answers
34 views

Vacuum Equalization

If I have two evacuated chambers each 10m on a side. Both are strong Vacuums but one is a slightly lower pressure than the other (A is the lowest pressure vacuum [ 10x-10 tor], B is the slightly ...
Marco Chacon's user avatar
1 vote
0 answers
69 views

Most probable velocity of a mixture of gases [closed]

We have the average, root mean square, and most probable velocities of a gas as $v_{av}=\sqrt\frac{8KT}{\pi m}$ ; $v_{rms}=\sqrt\frac{3KT}{m}$ ; $v_{mp}=\sqrt\frac{2KT}{m}$ For a mixture of two ...
Chirag Swarnkar's user avatar
2 votes
0 answers
44 views

How do steam work in micro gravity?

Imagine an astronaut spills boiling hot coffee inside the orbiting space station, where do the steam go? I mean the coffee will likely form into many many balls but they at still very hot!
user6760's user avatar
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0 votes
0 answers
97 views

How many degrees of freedom does a diatomic and triatomic molecule have at high temperatures?

I understand that a diatomic molecule has 3 translational and 2 rotational degrees of freedom. But since there is only 1 vibrational mode associated with a diatomic molecule and 1 vibrational mode is ...
Srijan Das's user avatar
0 votes
2 answers
133 views

Is the equation for degrees of freedom $f=3N-k$ valid for all cases?

Consider the example of a linear triatomic molecule. Now at low temperatures, where we can exclude vibration, quite clearly degrees of freedom, $f=5$, with 3 translational and 2 rotational degrees of ...
Srijan Das's user avatar
3 votes
1 answer
161 views

Non-isentropic expansion of an ideal gas?

Consider an ideal gas in a piston, where the piston head moves to increase the volume of the piston from $V_1$ to $V_2$. If the piston head moves and $v\ll v_s$ with $v_s$ the speed of sound in the ...
David's user avatar
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5 votes
1 answer
221 views

What is the most general and accurate real gas equation?

I've been presented in my thermodynamics course with both the ideal gas and Van der Waals state equations for the study of gases, being the latter more accurate in measurement than the first one. ...
Takopako's user avatar
  • 117
1 vote
1 answer
103 views

The viscosity of Natural gas

At low pressures, gas viscosity increases as temperature increases, which is mainly due to increase in the intermolecular collision that is caused by an increase in molecular friction. However, at ...
Ulvi Rahimov's user avatar
1 vote
1 answer
121 views

Bulk modulus for a gas that obeys van der Waals equation

I was searching for an expression for the bulk modulus $B$ for a gas that obeys the van der Waals equation ("van der Waals gas" from now on). Since for an ideal gas we have that $B=\gamma P$ ...
Ciro's user avatar
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0 votes
0 answers
28 views

How does gas flow change with gas composition?

How does gas composition affect gas flow rate with all other parameters being constant? I am trying to calculate the flow rate of raw biogas with 63% CH4 and 37% CO2 relative to purified biogas with ...
Samuel Soroaster's user avatar
-1 votes
1 answer
113 views

Why work is calculated by $Vdp$ when volume is constant in thermodynamics? [duplicate]

Why work is equal to $-VdP$ when volume is constant? Doesn't that imply that work is equal to 0? Isn't work a result of volume change?
Unicornsatemee's user avatar
1 vote
1 answer
30 views

Collision frequency of a 3D object in a container

Might be a silly questions but I had a thought while learning about the collision frequency of gas molecules on a single surface of a container using kinetic theory. For a 3D object in the container, ...
Yourhelpismuchapprecciated's user avatar
0 votes
2 answers
72 views

Evaluating Maxwell Relations with Constant Entropy for Arbitrary EOS

If you were given a Gas Equation of State, whether that be Ideal, van der Waals, Redlich-Kwong, or some more complex EOS, and you needed to evaluate a Maxwell Relation such as $\left(\frac{\partial p}{...
Jacob Ivanov's user avatar

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