# What is Perfect gas: Definition and 23 Discussions

In physics and engineering, a perfect gas is a theoretical gas model that differs from real gases in specific ways that makes certain calculations easier to handle. In all perfect gas models, intermolecular forces are neglected. This means that one can neglect many complications that may arise from the Van der Waals forces. All perfect gas models are ideal gas models in the sense that they all follow the ideal gas equation of state. However, the idea of a perfect gas model is often invoked as a combination of the ideal gas equation of state with specific additional assumptions regarding the variation (or nonvariation) of the heat capacity with temperature.

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1. ### B Applying Bernoulli's equation to problems involving a perfect gas

I would like to know the opinions of experienced forum users regarding an issue that seems to happen often in problems: namely, applying Bernoulli's equation to perfect gas. Is it permissible to do so, even if only to find reasonable estimates? Two examples I found out might be: - The problem...
2. ### I Variation of air temperature with altitude

Considering the approximation of perfect gas, I don't understand why at higher altitude the temperature is lower. Intuitively it is clear to me, but I do not understand the kind of transformation that takes place; the gas is free to expand and the pressure too is not constant, since it decreases...
3. ### I Exploring Work Done in Quasi-Static & Non Quasi-Static Expansion

I'm wondering what's the difference between work done on quasi-static and non quasi-static expansion. In a quasi-static process, the gas inside the system must do a work to "extend". However, in a non quasi-static process, where the gas inside the system doesn't move fast enough to "push" the...
4. ### Engineering System Constants for Perfect Gas

Q) I have to explain the relationships between system constants for a perfect gas. Hi can somebody explain this to me. I am kind of confused what this means and where to start and what to do. Also not 100% sure what a perfect gas is.
5. ### Engineering Differences between an Ideal gas and a perfect gas?

Is this right for difference between idea gas and perfect gas. trying to get it into head but can't find simple explation.Idea gas it is a fictious matter that follows the PV=nRuT or PV = mRuT equation, which has predermined conditions of ideal conditions of the the gas. As temperature for...
6. ### Maxwell-Boltzmann distribution for the simulation of a perfect gas

I'm currently programming lots of physics simulators in DHTML, and my next step would be simulating a perfect gas behavior at a molecular point of view, bouncing inside of an HTML canvas. For this reason, I came across "Maxwell-Boltzmann's law of distribution"(for speed, which I only studied...
7. ### I What is the difference between a perfect gas and an ideal gas?

What is difference between perfect gas and ideal gas?
8. ### I Perfect gas in a box with a piston

We have a perfect gas in a closed box. On the top of the box there is a piston. We know that the molecules of the gas exert a pressure on the piston. Now let us put twice as many molecules in this tank, so as to double the density, and let them have the same speed, i.e., the same temperature. At...
9. ### Quick question about perfect gas

Two different gasses (Helium and Cripton) are mixed up. We can assume the compound behaves as a perfect gas only if the atoms of He and Kr have the same average value of: Mass Momentum Velocity Kinetic energy Which one is correct? I can't figure it out.
10. ### Why is 2L used as the distance in the derivation of 1/3nMc^2 = nRT?

In the derivation the first step used F=Δmv/t and for t, they used t=2L/v where L is the distance between one end to the other end of the wall. But I don't understand why we use 2L as the distance. Isn't the force exerted by that molecule only for the very short period where the molecule is in...
11. ### What does the maximum work of a reversible expansion mean?

What does it mean by maximum work of an isothermal, reversible expansion of a perfect gas from initial volume Vi to final volume Vf at temperature T? I understand that heat enters the system during this expansion to ensure that no internal energy is lost but it doesn't really help in anyway...
12. ### Question about compressibility factor

At low temperatures, z falls below 1 and the reason for that is because the intermolecular interactions cause the pressure exerted to be lesser than expected. PVm/RT=z and since P is less than expected z drops below 1. However, as the pressure increases z increases to be above 1 because as P...
13. ### The work done by a perfect gas

Homework Statement An ideal gas at initial temperature T1 and pressure P1 is compressed by a piston to half its original volume. The temperature is varied so that the relation P=AV always holds and A is a constant. What is the work done n the gas in terms of n (moles of gas) R (gas constant)...
14. ### Polytropic process vs perfect gas eq

The polytropic law states: (1) P1V1n = P2V2n The perfect gas equation states: PV = mRT --> P1V1/T1 = P2/V2/T2 If T1 = T2 then (2) P1V1 = P2V2 So, how can equation 1 and 2 both be true for the same gas? If the gas follows a polytropic process, where n ≠ 1, how can 2 be...
15. ### Thermodynamics perfect gas law

Homework Statement Air inside a sealed tin can is initially at a pressure of 200 kPa and temperature of 20 ◦C. The tin can is known to burst at a pressure of 500 kPa. If the pressure is raised through heating, at what temperature will it burst? If you used an air compressor to pump up the...
16. ### Determine the unknown property of a perfect gas

Homework Statement two hundred seventy grams of argon at a pressure of 160kpa and a volume of 1.3 m^3. Homework Equations pv=nrt The Attempt at a Solution (160^3)(1.3) = (.27)(8.31)(t) 208=2.2437t t=92.7
17. ### Determine the unknown property of a perfect gas

Homework Statement a gas in 3-L container at a pressure of 300kpa and a temperature of 700 degrees celsius, and with a mass of .66 g. Homework Equations pv=nrt The Attempt at a Solution (300)(v)= (.00066 kg)(8.31)(191906 k) = 3.51 im not sure what conversion needs to be...
18. ### Discussion about thermal chemical-equilibrium gas and calorically perfect gas

Homework Statement Calculate the percent difference of P2/P1, T2/T1, and ρ2/ρ1 between the CPG assumption and the thermal-chemical equilibrium assumption. Which percent difference is the lowest and what could be the possible reason? U1=4000 m/s Altitude=60 km R=8314 N m/(kmol K) P1=21.96 Pa...
19. ### Entropy change for isothermal expansion of a perfect gas

Homework Statement At a constant temperature, 0.85 mol of an ideal gas changes its pressure from 350 Torr to 125 Torr. Calculate the entropy change for this expansion process. Homework Equations Ideal gas: PV=nRT ΔS = nRln(Vf/Vi) The Attempt at a Solution I'm stuck on how to...
20. ### Thermodynamics perfect gas Question

Homework Statement The partition function for a perfect gas containing N monatomic particles of mass m at a temperature T is Z =(1/N!)*VN[2(Pi)mkT/h2]3N/2 (2a) Use this partition function to find the molar Helmholtz free energy, molar internal energy and molar heat capacity at constant...
21. ### Gravity's Impact on Perfect Gas Flow in Constant-Area Duct

Homework Statement Consider a perfect gas flowing in a constant-area. Duct adiabatically and without friction. Changes in state come about as the result of changes in elevation in the Earth's gravity field. The z-direction is away from the center of the earth, and hence gravity acts in the...
22. ### Entropy of a perfect gas at 0 kelvin

Hello, I'm still trying getting familiar with the concepts of statistical mechanics and thermodynamics , and there's this equation for S of an ideal system, which somehow perplexes me. Suppose the ideal gas is composed of N indistinguishable atoms , then : S = \frac{U - U_{0} }{T} + k Ln...
23. ### Solving the Perfect Gas Equation for Volume at Sea Level and 2000m

Hi, I'm not sure how to do the following. Could someone help me out? Q. At sea level, where the barometric pressure is 101.3 kN/m^2 and the temperature is 20 degrees celcius, a balloon is filled with 2.5 kg of hydrogen also at 20 degrees celcius. (i) Find the volume of the balloon at sea...