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What is difference between perfect gas and ideal gas?

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In summary, a perfect gas (or ideal gas) is a gas that follows the equation pV = nRT exactly under all conditions. While physicists use these terms interchangeably, engineers distinguish between them. In chemical engineering, an ideal gas is considered as the limiting behavior of a real gas at very low density, satisfying the ideal gas equation locally. The specific internal energy and enthalpy of an ideal gas only depend on temperature, while heat capacity, viscosity, and thermal conductivity are also functions of temperature. On the other hand, a perfect gas has a constant specific heat, while in an ideal gas it varies with temperature. From a kinetic theory perspective, an ideal gas is one where constituent particles have a shorter mean free path compared to the

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What is difference between perfect gas and ideal gas?

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@Chestermiller can fill in the details better than me.

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I want to know about it used in engineeringDrClaude said:

@Chestermiller can fill in the details better than me.

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1. At thermodynamic equilibrium, ##pV=nRT##

2. In a system not at equilibrium (experiencing an irreversible process), the gas satisfies the ideal gas equation pv=RT locally, where v is the specific molar volume. The pressure, specific volume, and temperature may be varying with spatial position and time.

3. The specific internal energy and specific enthalpy are functions only of temperature (and approach those of the real gas at very low density)

4. The heat capacity at constant volume and the heat capacity at constant pressure are functions of temperature, but do not depend on pressure.

5. The viscosity and thermal conductivity are functions of temperature but not pressure.

6. The entropy includes the effect of temperature on heat capacity.

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Yes, that's correct. And I considered not including #3, but, for a neophyte to thermodynamics, I felt it would helpful to include.Lord Jestocost said:

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I haven't got the difference between ideal gas and perfect gas?

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We're still waiting for a Physicist to respond with their version of an ideal gas and perfect gas. We engineers use ideal gas and perfect gas interchangeably. Anyway, you said you were more interested in the engineering definition (which I gave).Death eater said:I haven't got the difference between ideal gas and perfect gas?

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You have given the characterstics of ideal gas, they are true but I needed how can we differentiate between ideal and perfect gas?Chestermiller said:We're still waiting for a Physicist to respond with their version of an ideal gas and perfect gas. We engineers use ideal gas and perfect gas interchangeably. Anyway, you said you were more interested in the engineering definition (which I gave).

I know one of the difference, it is that in ideal gases specific heat vary with temperature but in perfect gas specific heat is constant. I wanted to know more about it.

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Like I said, I'll leave it up to Physicists to provide their version of things. You have our answer from us engineers.Death eater said:You have given the characterstics of ideal gas, they are true but I needed how can we differentiate between ideal and perfect gas?

I know one of the difference, it is that in ideal gases specific heat vary with temperature but in perfect gas specific heat is constant. I wanted to know more about it.

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From point of view of kinetic theory, one can define an ideal gas as a gas whose consituent particles have a mean free path which is much shorter than the typical space-time scales upon which the macroscopic properties of the gas changes. This implies equilibration (or relaxation) times much shorther than the typical timescales for changes of the macroscopic properties. Then the motion of the gas can be described well with ideal hydrodynamics, which implies that the gas is, on the resolution of macroscopic space-time scales, always in local thermal equilibrium.

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vanhees71 said:

From point of view of kinetic theory, one can define an ideal gas as a gas whose consituent particles have a mean free path which is much shorter than the typical space-time scales upon which the macroscopic properties of the gas changes. This implies equilibration (or relaxation) times much shorther than the typical timescales for changes of the macroscopic properties. Then the motion of the gas can be described well with ideal hydrodynamics, which implies that the gas is, on the resolution of macroscopic space-time scales, always in local thermal equilibrium.

I am confused after reading. I don't know what it is trying to say.

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Yikes. This is the same as what we engineers assume.vanhees71 said:

From point of view of kinetic theory, one can define an ideal gas as a gas whose consituent particles have a mean free path which is much shorter than the typical space-time scales upon which the macroscopic properties of the gas changes. This implies equilibration (or relaxation) times much shorther than the typical timescales for changes of the macroscopic properties. Then the motion of the gas can be described well with ideal hydrodynamics, which implies that the gas is, on the resolution of macroscopic space-time scales, always in local thermal equilibrium.

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According to the author your book, he defines a perfect gas as an ideal gas with constant heat capacity.Death eater said:View attachment 231708

I am confused after reading. I don't know what it is trying to say.

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Now I am more confused. What is perfect gas?Chestermiller said:According to the author your book, he defines a perfect gas as an ideal gas with constant heat capacity.

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I don't know how I can say this more precisely. Sorry. My advise is to not obsess over the difference, and to continue on with your learning.Death eater said:Now I am more confused. What is perfect gas?

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Ok, thanks any way for your tineChestermiller said:I don't know how I can say this more precisely. Sorry. My advise is to not obsess over the difference, and to continue on with your learning.

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Death eater said:Now I am more confused. What is perfect gas?

In Chapter III “SYSTEMS OF ONE COMPONENT” of the book “MODERN THERMODYNAMICS BY THE METHODS OF WILLARD GIBBS” by E. A. Guggenheim one finds:

“

for given

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