[tvtokyo]

I just have a question to pounder
Why cant we have an "adiabatic isobaric free expansion". I mean what are the factors and points that we have to exaplain.
adiabatic = q=0   and isobaric means constant pressure while free expansion means work done is 0. How do i link them?
Thanks.

[mjc123]

You can't have an isobaric expansion, unless you raise the temperature so V₂/T₂ = V₁/T₁. That can't be adiabatic because you need the energy to raise the temperature.

[mjc123]

It may be clearer on a graph. As you can see, an isobaric expansion must involve a temperature rise. For an adiabatic expansion, however, the work must come from the internal energy, so temperature falls. For an equilibrium adiabatic expansion, the line follows PV^γ = constant. If P_ext < P_gas, the work done is less and the temperature drop is less; in the limit of zero work the line will coincide with the isotherm. But I hope you can see it will never coincide with the isobar.