# Thermodynamics basic concepts

1. Sep 18, 2014

### iScience

*edited*

Just realized that's not what i wanted to ask, sorry.

New Question: What is an irreversible adiabatic process? is it when the net q(sys) remains the same but there is heat transferred within the system?

Last edited: Sep 18, 2014
2. Sep 18, 2014

### Staff: Mentor

No heat enters or leaves he system at any time during the process, and the deformation is rapid enough that the process cannot be considered quasi-static. Once the final state is attained, there is no way of getting the system back to the initial state without also causing a change in the surroundings.

Chet

3. Sep 22, 2014

### Andrew Mason

Just to add to what Chet has said, you could think of an irreversible adiabatic expansion as a dynamic process in which one part of the system does work on another part, which takes the system out of equilibrium. Since it is adiabatic, the work done has to be at the expense of the system's internal energy. When the system returns to equilibrium the energy gained by the part on which work was done is distributed back to the system as a whole. This could be viewed heat transfer within the system.

A free adiabatic expansion of a gas into an empty chamber is an example of such a process. When the throttle valve to the empty chamber is opened, the gas expands rapidly. Gas molecules escaping through the throttle valve experience an increase in kinetic and, possibly, potential energy (where there are intermolecular forces). The gas, effectively, does work on itself. It occupies more volume but has not had to push anything out of the way to make room. So it does no work on its surroundings. When everything reaches equilibrium, the gas must have the same internal energy as it had before expansion (first law).

AM

4. Dec 2, 2014

### Sanky123

What is differece between free expansion and ordinary expansion ??

5. Dec 2, 2014

### Matterwave

Free expansion means there's no external pressure or membrane inhibiting the expansion. In other words, a free expansion would be an expansion into a vacuum.

6. Dec 2, 2014

### Sanky123

But how is this possible?

expansion in vaccume?

7. Dec 2, 2014

### Matterwave

For example, if you have a container which is at first separated. One side of the container has a gas, and the other side is a vacuum. When you remove the separating membrane, you have "free expansion".

8. Dec 2, 2014

### Sanky123

Ok..,
if we have to take into consideration power output,

then which will be effective one?

9. Dec 2, 2014

### Sanky123

Or if we have to consider work-done?