# Tagged Questions

A gas that behaves as randomly moving, non-interacting molecules. This allows a simplified equation of state.

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### What was the pressure of the Universe, when the CMB was 300K?

I suspect, at the time when stars didn't exist yet, we could calculate with largely homogeneous Hydrogen-Helium mix. Unfortunately, the sources I've found on google aren't really detailed.
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### Why does depth and height replace volume in this problem? [on hold]

In the following problem, why does H/𝛿 replace V/V? The two ratios have different units. Is there something I'm missing here?
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### How to find the change in internal energy for a gas? [on hold]

So I'm given this problem, and for some reason when I solve for Q and delta U my answer is off, should be $\Delta U = 249.3J$ and $Q = 415.5J$ ...
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### Maxwell's distribution analogue for angular velocity

Consider hydrogen ($\mathrm{H_2}$) as an ideal gas. We know that distribution of translational velocities is given by Maxwell's distribution. However our gas is diatomic, which means every molecule ...
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### How to calculate static air temperature

Let's suppose I have an airplane flying at an unpecified altitude and the following data are given: Flight Mach number: $M=0.76M$ Ground speed: $v_{kts}=470kts$ My goal is to estimate the air ...
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### Consideration on the total entropy variation for 2 ideal gases

Let's consider an isolated container containing a mole of an ideal monoatomic gas $A$ and a mole of a biatomic gas $B$, separated by an ideal piston (hermetic). The gases slowly exchanges heat and the ...
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### Rate of collision of gas molecules

On what factors does the rate of collisions of gas molecules with walls of a container depends? I know one would be temperature but are there any other factors like density,pressure,volume etc. I ...
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### How Quickly Do Gasses Mix?

When I pick up my scuba tanks from the dive shop, I measure the nitrogen and oxygen levels in it. I check that they are close to what I specified and calculate the maximum depth it's safe to go to to ...
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### 'Equations of State' - is it wrong to derive dynamic relationships from these equations?

When we speak of 'Equations of State' I believe we are most often referring to a steady state equilibrium relationship between particular state variables. Am I wrong? For example, the famous ideal ...
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### Relation between entropy and internal energy

I am confused as to what is the relation between entropy and internal energy. Entropy is always presented as a measure of the randomness in a system. So when we supply heat to a well insulated system ...
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### Compressibility factor and deviation from ideal gas behaviour

I have recently started to study the deviation of ideal gas behavior. The source from which I am reading doesn't give me an intuitive understanding of the compressibility factor. I dont understand how ...
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### Why don't air cool over time?

Say you have a balloon full of a type of gas, it is completely isolate from everything else. Let the temperature of the gas be 20 degrees (or any temperature, it doesn't matter) Now, the ballon is ...
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### Using the ideal gas law to figure final pressure [closed]

I'm studying for the GRE and I'm happy with Charles', Boyle's and Gay-Lussac's laws. I'm doing some questions on the ideal gas law. Please hear me out. This may come across as a homework style ...
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### Mixed Gas Absorbtion

Consider a gas misture that contains two type of atom, A and B. The gas is in equilibrium at temperature $T$. If on the surface of the gas container there are M sites that can absorb an atom gas, and ...
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### Work done by an ideal gas expressed as change in potential energy of fluid

I get confused in problems where it is necessary to evaluate the work done by a gas that someway moves a mass. I'll make an example. Consider the tube containing mercury and an ideal gas in A (...
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### Ohnesorge Number - why square root?

I understood the Weber number, but why would the Ohnesorge Number go like this: $$Oh = \frac{\text{viscous forces}}{\sqrt{\text{inertia \cdot surface tension}}}$$ Why the root? There seems to be no ...
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### Does a reversible heat engine exchanging heat with an ideal gas that does a transformation imply that transformation is reversible?

Consider a reversible heat engine working between two sources. Suppose that one of the sources is a thermostat, while the other is an ideal gas which follows a transformation and exchanges some heat ...
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### Newton's 2nd Law with Dirac Delta, as a way to derive the Ideal Gas Law

I'm trying to derive the ideal gas law from first principles, namely that a particle bouncing off a wall will exert a force on the wall. Newton's second law $F=\frac{dp}{dt}$ relates the force an ...
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### What VOLUME does exactly the $V$ term in ideal gas equation represent?

According to kinetic theory of gases 'the actual volume occupied by the gas molecules are negligible in comparison to the volume of the container.' I believe that this assumption is significant ...
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### Behavior of atom's wave packets in a gas

It is my understanding that the wave packet of a free localized particle spreads with time. My question is what is the best description of the particles in a gas inside a closed container: Do they ...
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### Kinetic gas theory: How large are rotational and vibrational energy for a linear diatomic molecule?

Let's say one has given a temperature of a simple linear diatomic gas like Hydrogen $H_2$. From the temperature one knows the energy of the gas, but how does this energy "split up" to the different ...
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### How does pressure change over time in an open box?

Imagine that you have a 1 cubic meter metal box with two 20 mm diameter holes. One of them is connected to an air-compressor that constantly pressurizes the inside of cube. Let's say 5 atm. The other ...
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### Deriving Ideal Gas law from Hamiltonian Mechanics

I just don't understand the explanation in Wikipedia. Is there a nice & elegant way of arriving at the Ideal Gas Law from Hamilton's Equations?
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### Ideal gas law: Will the piston move at all?

We have the following experimental setup: Before the experiment starts: $$p_1=p_2; \space V_1=V_2; T_1=T_2+\Delta T$$ The experiment starts and both the containers are heated so that the ...
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### Intuitive explanation of the shape of the Maxwell-Boltzmann distribution

At higher temperatures (for an ideal gas), the Maxwell-Boltzmann distribution is spread more widely and has a lower maximum. At lower temperatures, the spread is much more narrow and the peak is much ...
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### Ideal gas equation and atmosphere of Venus

I'm teaching myself some basics of the ideal gas law and working out simple density equations for atmospheric gases at various altitudes. When I applied the gas law to Venus' atmosphere at its ...