Questions tagged [ideal-gas]
A gas that behaves as randomly moving, non-interacting molecules. This allows a simplified equation of state.
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Why does an isothermal expansion require more energy?
Let's say we have two completely identical cylinders of some ideal gas (same $P,V,T,n$, etc...), and we just want to double each one's volume.
First Cylinder
The first cylinder undergoes a simple ...
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1answer
12 views
Calculation of humidity ratio by vapor partial pressure
I've been looking around for a way to calculate the humidity ratio by the partial vapor pressure and the atmospheric pressure of the environment.
I found a procedure for such calculation on ...
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1answer
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$pV=nRT $: Is this rudimentary proof correct in its assumptions?
I had a quick check in the help page (there wasn't much info on these
types of questions). It looks to be allowed
I know this doesn't technically constitute as proof (since it assumes other equations ...
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2answers
34 views
Why do some gases have fewer degrees of freedom at same temperature?
I am trying to understand the degres of freedom for gases.
Air has 5 degrees of freedom at room temperature but why does Argon, $Ar$ have 3 degrees of freedom while $O_2$ has 5 at the same temperature ...
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How long does it take for 1 mole $H_2$ at STP to diffuse to a density of one $H_2$ molecule per $m^3$ in interstellar space?
One can read here:
The molar volume, or volume of one mole of gas, depends on pressure and temperature and is 22.4 liters - at 0 °C (273.15 K) and 1 atm (101325 Pa), or STP (Standard Temperature and ...
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1answer
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Can you reach higher efficiencies of the Otto cycle by changing the sequence slightly?
If we take the common Otto cycle we have two isochoric and two adiabatic processes, plus exhaust & intake stroke.
Would it be more efficient to do the following:
Instead of cutting off the ...
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1answer
20 views
Calculating Temperature of boiling water using constant volume gas thermometer
Why different gases give slightly different temperature at same pressure in a constant volume gas thermometer?
My book says we should lower the amount of gas in the thermometer to get perfect result
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1answer
31 views
Pressure - temperature relationship in constant volume with high temperature and density
For the coating, it is necessary to pour 40 ml of liquid in a closed container with a volume of 80 ml and place it in an oven at a temperature of 200-300 °C .My question is whether, given the high ...
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1answer
56 views
Understanding the physical process that takes place in this problem about ideal gases
I am faced with the following problem:
A cylinder containing $n_{0} = 4$ moles of ideal monoatomic gas, at temperature $T_{0} = 280\ \mathrm{K}$ and pressure $p_{0} = 150\ \mathrm{kPa}$, is equipped ...
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1answer
68 views
Small $N$ ideal gas entropy and extensive entropy: Finite $N$ Sackur-Tetrode and Gibbs Paradox
In the standard derivation for Sackur-Tetrode, the accounting for the indistinguishability of ideal gas molecules adds an extra factor of $N!$ in the partition function. This is usually approximated ...
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1answer
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How to derive that $\delta w = - PdV$?
I am not understanding how to derive this particular expression, which relates the inexact differential of work to the exact differential of volume,
$$\delta w = -PdV $$
My attempt:
Reversible work ...
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5answers
354 views
Why is there a special connection between entropy and heat?
As I understand it:
$dS = \frac{1}{T}dU + \frac{p}{T}dV$
(for a thermodynamic system where $dN=0$) and since for an ideal gas $pV=Nk_BT$ and $U=C_VT$ we can say
$dS = \frac{C_V}{U}dU + \frac{Nk_B}{V}...
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3answers
36 views
What is the difference between a macrostate and multiplicity?
The entropy of a system of an ideal gas depends on the external parameters $U, V, N$.
I always thought entropy is defined by a certain macrostate, which is a set of given external conditions like ...
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1answer
44 views
Does the ideal gas law apply to gases which consist of more than one atom?
In the derivation of the ideal gas law, one sets for the average kinetical energy $f = 3$ degrees of freedom. This refers to the transition in x,y,z axes. This is true for gases, which consist of only ...
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2answers
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Given pressure in Pascals and temp in Kelvin what equation determines the weight of a volume of air? [closed]
I'm trying to determine how many kg of air that a Zeppelin displaces.
The volume of the airship is 58142.1 meters cubed.
The temperature of the air is 276.26 kelvin.
The pressure in pascals is 42,178....
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Temperature change of an ideal gas during an adiabatic free expansion
During an adiabatic process there is no heat exchange and thus, q = o.
During a free expansion no work is done and so w = o.
Since q = U + w, thus we can say that during the overall process, change in ...
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3answers
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For a gas in an open vessel, should the volume of gas be the volume of whole universe?
In the ideal gas equation $PV=nRT$, $V$ is defined as free space available to the gas. In an open vessel in which temperature is maintained constant, shouldn't the volume $V$ of the gas be the volume ...
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102 views
Work done “by gas” in a isobaric process?
Starting from First Law of Thermodynamics, we have
ΔQ = ΔU + ΔW
Where, ΔW is the work done "by gas" on the surrounding.
Now, for an isobaric process, it is given by
ΔW = ∫PdV = PΔV
here ...
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1answer
24 views
What exactly is the use of partial pressure of a component?
Is partial pressure the actual pressure a component contributes in a mixture? What is the physical essence of partial pressure?
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1answer
47 views
Why is volume of a gas in an open container assumed to be constant?
I've read this in a book
When air is heated in an open vessel, pressure is always atmospheric pressure, and volume of the gas is constant.
How is volume of the gas constant in this case?
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1answer
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Rate of change between radius and temperature in a spherical balloon with difference of pressure proportional to the radius
I have an spherical ballon filled with an ideal gas such that the difference of pressure between the interior $(P)$ and the exterior $(P_0)$ is proportional to the radius of the balloon:
$$P-P_0 = \xi ...
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4answers
498 views
Deriving ideal gas law from Boyle and Charles
My textbook states
Notice that since $PV = \text{constant}$ and $\frac{V}{T} = \text{constant}$ for a given
quantity of gas, then $\frac{PV}{T}$ should also be a constant.
I tried to prove this, but ...
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1answer
64 views
Why do we use RMS speed rather than just taking the average of absolute value of the speeds?
I get that negative values to cancel positive values, and that is the reason why we don't do a direct average. So why don't we just use the absolute value mean of the speed?
If I have one gas particle ...
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1answer
32 views
In Charles' law how to change volume in order to observe the change in temperature?
At constant pressure,
$$ V\propto T$$
Letting the piston freely moving fixes the pressure of the gas to the atmospheric;
then heating the gas causes the $T$ to increase,
this causes the $V$ to ...
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2answers
77 views
Why is the temperature of a gas proportional to the average kinetic energy of its particles?
I'm studying the kinetic theory of gases I managed to derive that pressure is inversely proportional to volume and directly proportional to the average kinetic energy of the gas particles. Similarly, ...
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2answers
80 views
Is a constant pressure adiabatic irreversible expansion possible?
We know that adiabatic law for an ideal gas is,
$$ PV^{\gamma} =C$$
the differential of this under constant pressure is,
$$ P \gamma V^{\gamma-1} dV = 0$$
Now, the pressure and volume can't be at all ...
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0answers
73 views
Ideal gas law vs van der Waals equation of gas
$$ ( P + \frac{n^2 a}{V^2})(V-nb) =nRT$$
is the van der Waals equation of state
and,
$$ PV=nRT$$
is the ideal gas law.
Similar to how I asked in this stack , prof. Moungi Bawendi says that as we drop ...
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1answer
42 views
What is the pressure at a random point inside container of an ideal gas?
In most textbooks and thermodynamic lectures, the pressure is defined as the force on the walls of containers due to the incassecant beating of gas molecules divided by the area of the wall. Now, ...
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1answer
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Defining the Ideal gas thermometer
At 2:22 of this video , the prof. Moungi bowendi motivates the ideal gas law by saying that
$$ \lim_{ p \to 0} p \overline{V} = f(T)$$
That is if we drop pressure and see how it changes the volume, ...
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Entropy for perfect gas, to show that $\mathrm{d}S = c_v\frac{\mathrm{d}p}{p} + c_p\frac{\mathrm{d}V}{V}$
I am trying to show that for ideal gas:
$
\mathrm{d}S = c_v\frac{\mathrm{d}p}{p} + c_p\frac{\mathrm{d}V}{V}
$
But I keep getting an additional term $\frac1T\left(\frac{\partial U}{\partial V}\right)_T\...
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2answers
54 views
Can Bose–Einstein condensate (BEC) take up no space?
If multiple bosons can occupy the same state, does that mean you can put an infinite number of them in a fixed container at zero temperature without pressure.
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2answers
51 views
Does volume change as much as pressure changes in $pV=nRT$?
If I have an ideal gas where $pV=nRT$ applies, and I compress the gas to half the volume, does this mean that the pressure has necessarily doubled? And if it did, that should mean the temperature is ...
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3answers
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Looking for an alternate derivation of collision frequency of ideal gas molecules with the container walls
I've learnt how to calculate the collision frequency of ideal gas molecules with the walls of container using Maxwell Boltzmann distribution given as
$$ f=\frac{1}{4} n\langle v\rangle$$
However I was ...
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6answers
173 views
Change in temperature of a moving gas container which is suddenly stopped
Although this question has been asked many times here, I haven't found a satisfactory detailed quantitative answer.
The question is:
If an ideal gas container that is moving with a velocity $v$ is ...
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2answers
66 views
Why don't we take into consideration the rotation and vibration of gas molecules on the pressure of the gas?
While going through the derivation of how to calculate the pressure of an ideal gas we consider only the translation of molecules. Why don't we take into account that the molecules may rotate and ...
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3answers
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Doesn't the Ideal Gas Law contradict the First Law of Thermodynamics
Let's say that an ideal gas does work on a piston, thus increasing the volume of the gas in its insulated cylinder. The pressure of the gas is assumed to be constant; therefore, by the ideal gas law, $...
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3answers
48 views
Thermodynamics — Energy of system in ideal cases
In the books,it is stated that the energy of a gas system is purely Kinetic for an ideal monoatomic gas.
Why are energies such as nuclear energy not mentioned here?
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1answer
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Determining properties of air
Is there any way to theoretically obtain values of specific volume, internal energy, enthalpy and entropy of air, assuming it's an ideal gas?
Can it be done using ideal gas laws?
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1answer
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Shipping Products to a Low Air Pressure Area
We shipped a container of wet wipes packages by sea and when the container arrived to the port it was unloaded and the packages were verified to be ok.
Then, it was loaded to a truck and shipped to a ...
0
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1answer
73 views
Contradiction between the first law of thermodynamics and combined gas law
In the first law of thermodynamics, it is stated that:
$$\Delta U = Q + W$$
Which can be written as:
$$\Delta U = Q + P\Delta V$$
Since $\Delta U$ affects $U$ (internal energy), which itself affects ...
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3answers
89 views
Pressure in equations such as the Ideal Gas Law
When using the ideal gas law and other equations, are we assuming that the gas has uniform pressure (i.e. the pressure does not vary inside the gas)?
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How to calculate the probability of an enclosed gas migrating to one side of an enclosed box
Non-physicist asking.
I have a hollow enclosed 1cm-sided cube. It is filled with N mols of an ideal gas.
(1) What is the probability that for one infinitesimal moment, all the gas will occupy half of ...
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Kinetic Equation of Gas: Why is $T$ not the time of impact?
so i just learnt about about the derivation of Kinetic Gas Equation! In that derivation, and i have a question which i am trying to find the answer for but i can't find it anywhere on the internet!
In ...
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Chamber with semi permeable membrane
Consider two cases in a chamber in which gases are filled on both sides of a partition which acts a semi permeable membrane :
1.Hydrogen is filled on one side of the partition and it can move through ...
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0answers
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Is the entropy change due to particle insertion/deletion the same as increasing/decreasing the volume (or pressure) for an ideal gas?
Background:
Consider a pure monatomic ideal gas within a closed system undergoing a reversible, isothermal compression/expansion.
The fundamental thermodynamic relation is
$$d U = T d S - P d V + \mu ...
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2answers
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What is the origin of pressure of gas acting a surface beneath it?
I understand that the origin of atmospheric pressure is the weight of air.
Imagine if there is a cylinder consisting of two compartments separated by a frictionless piston filled with gas, the lower ...
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1answer
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Clarifying the relationship between pressure and temperature?
From the ideal gas law, we are aware that PV = nRT, which seems to suggest a direct relationship between pressure and temperature, or that as temperature increases, pressure increases.
In my geography ...
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3answers
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Temperature change in a gas tank on a car [closed]
There is a beautiful question I ran into:
A gas tank filled with gas at temperature $T$. The gas is at rest first. It is accelerated to a constant velocity of $V$. Assume the process is adiabatic.
...
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1answer
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Why does a given molecule is able to exclude 4 time of its volume in the correction term of Van der Waal's equation?
In the Van der Waal's equation in volume correction term, a given molecule is able to exclude 4 times of its volume from the volume of the container. Why is it so?
From the Wikipedia page on the topic,...
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1answer
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Thermal expansion coefficient and third law of thermodynamics
Thermal expansion coefficient is defined as:
\begin{equation}
\alpha=\frac{1}{V}\left(\frac{\partial V}{\partial T}\right)_p
\end{equation}
We can prove through the third law of thermodynamics that:
\...
