All Questions
Tagged with thermodynamics pressure
786 questions
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What is the pressure apllied to liquid in sealed tank?
I have a sealed tank positioned on a high surface filled with water and nitrogen gas above. Tank manometre shows pressure of 0.5 bar.
What is the pressure applied to the water in tank? Is it 0.5 or 1....
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Does the pressure in a pipe influence the mass flow?
A 50 MW generator cooled with hydrogen generates a power loss of 2.5 MW.
This heat output is dissipated by the gaseous hydrogen at a constant pressure of 0.98 bar. The hydrogen heats up from 15°C to ...
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Do gases speed up as they leave the barrel of a gun? If so why?
I am attempting to understand the exact physics behind the recoil in guns. I made an original post on reddit here specifically asking why gases exiting a barrel after the bullet leaves causes a sudden ...
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Henry's Law - When scuba diving, why is breathing pure $\rm O_2$ not the same as going to outer space?
In Short
I had a discussion with my dive instructor the other day. He said that for "decompression dives" you can cut down decompression time to 1/3 if you switch to pure $\rm O_2$ at 6m.
...
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Why is pressure independent of the mass of the particles of the gas?
Why is pressure independent of the mass of the particles of the gas? Wouldn't heavier particles hit the wall harder. Pressure is force per area, and force is related to inertia/mass. Doesn't this ...
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Hydrogen in soap bubble
I read somewhere that if hydrogen gas is passed through soap solution bubbles containing hydrogen are formed. My question is how these bubbles are stable! Hydrogen has much less density and mass than ...
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High Pressure Gas Scenario
Imagine a concept scenario in which there is a gas initially at standard atmospheric pressure contained in a standard mild steel cylindrical container of 10cm diameter and 1cm thickness. The pressure ...
user322011
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Free energy Functional and its Relation to Pressure and Chemical Potential
I am reading a paper and trying to follow along some of the mathematical steps and reasoning; however, I can't quite understand one aspect. The authors give an expression for the free energy ...
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Doubt with partial pressures
I have a conceptual doubt about partial pressures. Suppose you have a closed system composed of a gas mixture, say Argon and Helium. If they behave according to Ideal Gas Law, then the molar fraction ...
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Fid the coefficient of thermal expansion of liquid
Please explain why we get two different expansion for two different methods i.e. when we equate the pressure at Aand D ,and at C and B and which is correct and why because in book and at other ...
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Why aren't all irreversible processes isobaric?
I am slightly confused about graphs of irreversible processes. Firstly, they are difficult to find and whenever I find them the form is something similar to:-
I have read about the explanation given ...
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What is constant in an isobaric process, internal pressure or external pressure?
I was taking a course in thermodynamics, where the instructor started to derive the formula for work in case of isobaric process for an ideal gas
It stated W = -∫ P_ext dV
And then equated it with -∫...
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Differential geometry and the $P \vec A= \vec F$ equation?
How does one write
$$\vec F = P \vec A$$
(where $\vec F$ is the force. $P$ is the pressure and $\vec A$ is the area) in the language of differential forms? I'm confused cause $\vec F$ is a one form ...
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Pressure in a gas as it becomes a plasma
Let's say you have 1 mole of hydrogen, and you heat it to the point that the H-H bond breaks and you get free hydrogen atoms, and then fully ionized hydrogen ions + electrons.
When H2 becomes 2H (...
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Intuition behind entropy and its differentiation
I was reading the following paper about a better intuition of entropy and how it is connected to heat energy without the use of microstates:
The problem is when he assumed that volume is constant and ...
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Proof of pressure of ideal gas from first principles
Here's a question aimed at a deeper intuitive understanding of statistical physics and the theory of ideal gases, which has bothered me for quite a while.
Assume a billiard table 2D. The table has ...
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Pressure dropped in vacuüm chamber after vacuuming the chamber and closing it. How?
I was doing a leak test for a low vacuüm application by vacuuming a small chamber to 60 mbar and then measure the pressure for 16 hours at constant temperature. I chose 60 mbar to prevent evaporation ...
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A gas immersed in a higher-pressure gas: spherical shape?
I'm considering a bubble of gas of some arbitrary shape immersed in another gas of higher pressure. There is no gravity (and hence no buoyancy), the gases are ideal (so there are no attractive forces ...
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A combustion engine uses cylinders to compress air and fuel before igniting it
The piston moves up to compress the mixture before exploding and sending the piston down with great force.
Would there be any improvement if the piston were turned upside-down? This would mean the ...
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Maximum temperature of plasma according to $pT$ diagram
When I look at the graph, I can find maximum temperature of plasma (roughly 1eV at 10kPa). But you can get a lot hotter with plasma. Please, where is the mistake?
See: or See: https://www....
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Van der Waals derivation: How is the pressure term exactly derived?
The van der Waals equation is:
$$ \left(p + \frac{n^2 a}{V^2}\right)\left(V-nb\right) = nRT $$
I understand the volume term, it basically reduces the avalaible volume because the particles have volume ...
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Rankine Cycle $pV$ diagram
I was going through the $pV$ diagram of the ideal Rankine cycle and all of the images that I found on the internet and as opposed to the $TS$ Diagram, they tend to show the compression in the ...
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How do you calculate the fugacity for a Van der Waals gas at low pressure?
How can the fugacity of this state equation:
$$pV/(nRT) =1+ [b-a/(RT)] p/(RT)$$ be calculated? I've already tried to divide the pressure of that by that of an ideal gas, but somehow don't get far with ...
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Net force exerted by pressure
Why do the net force $K$ exerted by the pressure of
a hard sphere gas according to the Maxwellian distribution on the walls of the container
$A \subset R^3$ vanishes? (In the absence of external ...
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Slope of constant pressure line on $T$-$S$ plot
Is slope of constant pressure line is same or di in liquid region and super heated region for pure substance on $T$-$S$ diagram?
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Can we have constant volume, and pressure in a system?
I was given a system where heat was added to a mass of Nitrogen gas in a canister at constant pressure? And given the volume of the canister as 1L, I assumed that the gas would expand to fill the ...
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Static and stagnation enthalpy / pressure derivation for incompressible flow
I was wondering how one could derive the relationship between static and stagnation pressure in incompressible flow from the relationship between static and stagnation enthalpy.
It should be pretty ...
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Understanding the shape of Carnot loop in the $p$-$V$ plane
The area enclosed by a loop is the total work done. If you draw a square, isn't that the maximum amount of work done possible instead. Why is the isothermal/adiabatic path the most efficient instead ...
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What happens when you shake a coke bottle too hard?
I've been thinking about this recently :
what happens when you shake a coke bottle too hard?
I know that shaking a coke bottle and opening it would release the coke. So if I tried it, what would ...
user333418
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Why does the air pressure not increase when I shake a coke bottle?
I tried this experiment lately and this happened, I shook a coke bottle and its air pressure remained the same but the coke came squirting out when I opened the lid. How is this possible?
user333186
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Does the air pressure inside a box remain the same after it is sealed?
Let's assume that the pressure is 1 atm outside the sealed box. I think that the pressure inside the box will be the same at 1 atm. But why?
Isn't the giant column of air above causing pressure ...
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Why is the pressure inside the bottle lower than atm pressure?
When a balloon is placed inside a bottle (covering the entranace), it will not inflate, since the bottle is already filled with air particles with no escape route. When you punch a hole in a bottle, ...
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Pressure becomes zero for ideal gas?
During a reversible process:
$$du=dq-dw=c_vdT-Pdv=\left(\frac{\partial u}{\partial T}\right)_vdT+\left(\frac{\partial u}{\partial v}\right)_Tdv$$
From the above, I get $\left(\frac{\partial u}{\...
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What happens to water as it is increasingly compressed?
Imagine we put some volume of water in an infinitely strong container, and then start to slowly exert a force on the top of the water , with increasing pressure. What happens to the water over time? ...
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Bottomley's ice cutting experiment
In My textbook, it says about Bottomley's ice cutting experiment of regelation, that the latent heat required to melt the ice to water even at a lower melting point comes from the wire and the ...
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Why saturated vapor does not obey gas laws? [duplicate]
in my book it has mentioned "number of saturate molecules does not remain constant when the temperature changes(mass of vapor is not constant),therefor saturated vapor does not obeys gas law"...
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Non-Ideal Gas Question
I have been attempting to solve a problem involving a non-ideal gas. The gas is assumed to be non-ideal and hence modelled by the Van der Waals Equation, it is considered to be pure hydrogen gas and ...
user322011
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Why does the keg temperature rise after pouring a beer?
I have a refrigerated pony keg. Inside is pressurized CO2 and beer. Connected to the bottom of this keg is a weight and temperature sensor. According to these sensors when a beer is poured from this ...
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Thermodynamics and dalton's partial pressure law
By kinetic equation of ideal gas,
$$PV=\frac{1}{3}mNu_{rms}^{2}$$
Where,
$P$ is pressure $m$ is mass of molecule $N$ is number of moles considered and $u_{rms}$ is root mean speed.
In my book to prove ...
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How is Avogadro's law tested practically?
I was reading about Avogadro's law which states that
Equal volumes of all gases under the same conditions of temperature and pressure contain equal number of molecules.
My question is, how can one ...
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Why don't substances other than water ice show regelation?
We know that ice shows regelation,but why don't other substances like iron rods or wood show the same phenomenon? Is there something special about ice?
user325981
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Why do we need to consider the area under Volume axis to find the work done by a gas?
For a $P$ vs $V$ graph for gas, why do we need to consider the area under the volume axis for determining the work done by the gas? Can't we take the area under the pressure axis to find the work done?...
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In reversible process, why define $\delta W=-PdV$ instead of $\delta W=-VdP$?
For a reversible process, it is assumed that the external pressure $P_{ext}$ is infinitesimally different from internal pressure $P_{int}$.
So in reversible process, I can have $~P_{int}=P(V,T)~$ but ...
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How do we explain the motion of a time-reversed emptying balloon in vacuum?
Imagine a balloon filled with air, let loose in outer space. There is an imbalance of pressure pushing to the insides of the balloon, and this imbalance is the motor of motion. There is no pressure in ...
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Entropy for constant pressure
Is it valid to say that at constant pressure the entropy can be written as follows
$$S=\left(\frac{\partial U}{\partial T}\right)_{p}~?$$
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Why does water boil when vapour pressure is equivalent to atmospheric pressure?
I'm struggling to understand why water would suddenly evaporate in a vacuum. Does the water already posses enough energy to boil when the ambient pressure is zero?
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How to deal with cubic terms in Gibbs free energy?
Consider as a toy example a system with Gibbs free energy given by
$$G(p,T) = p^3 - 2p^2 - p + 2.$$
If I was to find the Helmholtz free energy, I would try Legendre transforming $F = G - pV$,
$$V = \...
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What would the pressure inside a leaking container be?
I had a question posed to us in Physics Class about determining the pressure inside a container when a volume of gas is expelled out of it at a contant rate, the question was as follows:
A Vessel of ...
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Confusion over definition of enthalpy as $h = f(p, T)$
I've often seen in textbooks that enthalpy (h) is specified as $h = f(p, T)$. We further go ahead in differentiating $h$ to get-
$$
dh = \frac{\partial h}{\partial T} dT + \frac{\partial h}{\partial ...
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Would lotion pumps work in a vacuum?
I'm just trying to understand how a lotion pump works. I watched this video and it's explained that it's due to the difference in air pressure.
https://www.youtube.com/watch?v=EJVL5zXIPLA&...
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