Andrew mason ideal gas law and adiabatic expansion problem

[sunnypic143]

Q1.

ADIABATIC FREE EXPANSION(unrestricted and free)
in vacuum gas a volume of gas is released
expected expansion proceeds withouut change in internal energy therefore temperature is contant (joule's law) . there is no pressure acting on this system threfore no work is done.
now out of 3 thermodynamic variables 2 (p & t) are constant with only v changing
what causes this change ? ie what factor accounts for this change of volume

Q2.
I've read about joule thompson effect , where releasing gases thru a narrow orifice into vacuum causes rapid fall in temperature leading to the condensation of the gas.(used in liquefaction of air)
Isnt this case similar to adiabatic expansion of gases in vaccum? If so there ought not be a temperature change.
So what causes the condensation of gases?

Q3.
Ideal gas laws
Most books define conditions for ideal behaviour as
--> no intermolecular interactions
--> negligibility of molecular dimensions(ie diameter of moleculke<<< inter molecular distances)

So we would expect real gases to approximate to ideal gases at high temperature and low pressures


However, I came across a book where it says another condition in the list
--> the kinetic energy of particles >>> inter molecular interactions
And example cited is dense gases with high temperatures
ie real gases approximate to ideal behaviour at high temperatures and high pressures

So which approach is correct? there is a lot of misconception on this subject at the place where i live and this is a question frequently asked in exams please help.

 

[Chestermiller]

Q1.

ADIABATIC FREE EXPANSION(unrestricted and free)
in vacuum gas a volume of gas is released
expected expansion proceeds withouut change in internal energy therefore temperature is contant (joule's law) . there is no pressure acting on this system threfore no work is done.
now out of 3 thermodynamic variables 2 (p & t) are constant with only v changing
what causes this change ? ie what factor accounts for this change of volume

The gas on one side of the barrier is at pressure, and the other side of the barrier has vacuum. So, when the barrier is removed, there is a pressure driving force for gas to flow from the high pressure side to the low pressure side.

Q2.
Ive read about joule thompson effect , where releasing gases thru a narrow orifice into vacuum causes rapid fall in temperature leading to the condensation of the gas.(used in liquefaction of air)
Isnt this case similar to adiabatic expansion of gases in vaccum? If so there ought not be a temperature change.
So what causes the condensation of gases?

This is very different from free expansion. In the high pressure chamber, the gas remaining has done work to force the gas ahead of it through the orifice. So its internal energy per unit mass has decreased.

Q3.
Ideal gas laws
Most books define conditions for ideal behaviour as
--> no intermolecular interactions
--> negligibility of molecular dimensions(ie diameter of moleculke<<< inter molecular distances)

So we would expect real gases to approximate to ideal gases at high temperature and low pressures However, I came across a book where it says another condition in the list
--> the kinetic energy of particles >>> inter molecular interactions
And example cited is dense gases with high temperatures
ie real gases approximate to ideal behaviour at high temperatures and high pressures

So which approach is correct? there is a lot of misconception on this subject at the place where i live and this is a question frequently asked in exams please help.

Real gases approximate ideal behavior at high temperatures and low pressures.