Is there any process adiabatic and isothermal?

[imnotadmin]

Homework Statement

Is it possible to have a process that is both adiabatic and isothermal.

Homework Equations

The Attempt at a Solution

I think the answer is no. Because when a system is doing an adiabatic process, the total energy of this system must be changed. For an adiabatic process, there is no heat transfer to or from the system. So the temperature of the system must be changerd.

But, an adiabatic process only means that there is no heat transfer to or from out side. So when the out side environment is doing work on the system and the system transfer whole work out of itself. the temperature of the system will be same. but i am not sure is this ture.

could somebody explane this for me?

Thanks.

 

[kuruman]

If a process is both adiabatic and isothermal, what form does the first law of thermodynamics take?

 

[Mapes]

Because when a system is doing an adiabatic process, the total energy of this system must be changed.

Why?

 

[imnotadmin]

If a process is both adiabatic and isothermal, what form does the first law of thermodynamics take?

thanks. I am not sure that I understand completely what u said. But I think u mean that there is impossible a process is both adiabatic and isothermal. That is because when outside environment doing work to the system, the internal energy must be changed. And work can be change to heat 100% but heat can not change to work 100%. Right?

but, if there is a cylinder (cacuum, use a spring to replace gas ), when the work is done by outside. The energy of spring must be changed. and, in a ideal environment, this spring can do 100% work to outside when release. In this process, there is no heat, only work. So is this an adiabatic and isothermal process?

I am confused. pls give me some advice. thanks.

 

[imnotadmin]

Why?

thanks.
when a system is doing an adiabatic process, there is no heat can trasfer from or to outside. so the total energy of this system must be changed.

 

[Mapes]

What about letting two gases mix, or a gas expand into an empty chamber? These processes can be made adiabatic and have no associated energy change.

 

[D H]

thanks. I am not sure that I understand completely what u said. But I think u mean that there is impossible a process is both adiabatic and isothermal.

That is not what kuruman asked. He asked a simple question. Try answering that simple question.

That is because when outside environment doing work to the system, the internal energy must be changed. And work can be change to heat 100% but heat can not change to work 100%. Right?

Wrong. What is the first law of thermodynamics?

 

[imnotadmin]

Why?

That is not what kuruman asked. He asked a simple question. Try answering that simple question.

delta U=Q+W, adiabatic process => Q=0, => delta U=W, so is impossible a process adiabatic and isothermal?

 

[imnotadmin]

What about letting two gases mix, or a gas expand into an empty chamber? These processes can be made adiabatic and have no associated energy change.

so? still confuesd...

 

[kuruman]

Remember that the change in internal energy ΔU is proportional to the change in temperature ΔT. What is the change in temperature, what is the change in internal energy?

 

[D H]

delta U=Q+W

Correct.

adiabatic process => Q=0, => delta U=W

Correct.

so is impossible a process adiabatic and isothermal?

Whoa! How do you draw that conclusion?

Hint: delta T=0 => delta U=0.

What does this say about work?

 

[imnotadmin]

adiabatic process

delta U=Q+W, and Q=0 => delta U=W

isothermal process

delta U=Q+W, and delta U=0, => Q=-W

combine these two factors, so conclusion is impossible a process adiabatic and isothermal. Right?

 

[Mapes]

adiabatic process

delta U=Q+W, and Q=0 => delta U=W

isothermal process

delta U=Q+W, and delta U=0, => Q=-W

combine these two factors, so conclusion is impossible a process adiabatic and isothermal. Right?

$\Delta U=0$ only implies $\Delta T=0$ for an ideal gas. Also, processes exist where the work and heat transfer are both zero, as I described above. The processes are both adiabatic and isothermal.

 

[D H]

adiabatic process

delta U=Q+W, and Q=0 => delta U=W

isothermal process

delta U=Q+W, and delta U=0, => Q=-W

combine these two factors, so conclusion is impossible a process adiabatic and isothermal. Right?

Wrong!

There is one number that is equal to its additive inverse. What is it? (i.e., solve $W=-W$ for $W$.)

 

[imnotadmin]

sorry, i don't know what u meant

adiabatic process
delta U=Q+W, and Q=0 => delta U=W
isothermal process
delta U=0
so if a process is adiabatic and isothermal, when the work done by system or at system, it is impossible to satisfy U=W and U=0

 

[D H]

Who said work was being done on the system? Your original question was

Is it possible to have a process that is both adiabatic and isothermal.

The answer to that question is definitely "yes".

 

[quasar_4]

Mapes was right.

In a free expansion problem, no heat is exchanged nor is any work done. Thus, dU = 0 for the system ...and so is dT... but it is a real system, and it does create new entropy. So, there is at least one example of such a process.

 

[imnotadmin]

yes! got it

thanks very much to all

 

[athithi]

check this...
http://www.goiit.com/posts/list/physical-chemistry-name-one-process-where-both-adiabatic-isothermal-916569.htm

 

[athithi]

check http://www.goiit.com/posts/list/physical-chemistry-name-one-process-where-both-adiabatic-isothermal-916569.htm

 

[imnotadmin]

check http://www.goiit.com/posts/list/physical-chemistry-name-one-process-where-both-adiabatic-isothermal-916569.htm

Thank you!

 

[passingthru]

In the OP, when you say "process" do you mean only reversible ones?