Irreversible isothermal Process Work External pressure not provided

  • #1
Aurelius120
152
16
Homework Statement
An ideal gas is irreversibly isothermally expanded from ##(8bar ,4L)##to##(2bar,16L)##to##(1bar,32L) ##Find heat.
Relevant Equations
NA
Screenshot_20231231_031131_Chrome.jpg

It is clear that the process is isothermal else it is not possible to find heat absorbed.
$$W=-P_{ext}(\Delta V)$$

However ##P_{ext}## is not given. How do I proceed?
I tried taking ##W=-(P_2V_2-P_1V_1+P_3V_3-P_2V_2)=\Delta(PV)## but it is wrong for obvious reasons.
 
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  • #2
The one solution I found uses
##W_1=-(2)(16-4)## and ##W_2=-(1)(32-16)##
##W=(W_1+W_2) bar.Litre=-4000J##
And ##Q=4000J##

How external pressure becomes ##2\ bar## and ##1\ bar## is beyond me. It also seems wrong that ##P_{ext}## should change in an irreversible process? That is like the only thing that is good about irreversible calculations.
 
  • #3
Sketch a PV diagram of the process. Do you know what an isotherm looks like for an ideal gas?
 
  • #4
Mister T said:
Sketch a PV diagram of the process. Do you know what an isotherm looks like for an ideal gas?
images.jpeg

Something like this correct?
 
  • #5
Looks like you've found the way!
Aurelius120 said:
How external pressure becomes ##2\ bar## and ##1\ bar## is beyond me.
A slow compression expansion.

Aurelius120 said:
It also seems wrong that ##P_{ext}## should change in an irreversible process?
A dramatic example would be an explosion.
 
Last edited:

1. What is an irreversible isothermal process?

An irreversible isothermal process is a thermodynamic process that occurs at a constant temperature and is irreversible, meaning that it cannot be reversed without affecting the surroundings. In this process, the system exchanges heat with its surroundings while maintaining a constant temperature.

2. How does work occur in an irreversible isothermal process when external pressure is not provided?

In an irreversible isothermal process where external pressure is not provided, work can still occur through other means such as expansion against a vacuum or through other external forces acting on the system. Work is defined as the energy transferred to or from a system by means other than heat transfer.

3. What are the implications of not providing external pressure in an irreversible isothermal process?

Not providing external pressure in an irreversible isothermal process can lead to changes in the system's volume and pressure, affecting the work done by the system. It may also result in different thermodynamic properties and behaviors compared to a process where external pressure is provided.

4. How is the efficiency of an irreversible isothermal process affected when external pressure is not provided?

The efficiency of an irreversible isothermal process can be affected when external pressure is not provided, as the lack of pressure control can lead to inefficiencies in work output. Without external pressure, the system may not be able to perform work as effectively, resulting in lower efficiency compared to a process with controlled external pressure.

5. Can an irreversible isothermal process with no external pressure be used in practical applications?

While an irreversible isothermal process with no external pressure may not be ideal for all practical applications, it can still be useful in certain scenarios where specific thermodynamic conditions need to be studied or simulated. Understanding the behavior of such processes can provide valuable insights into thermodynamic systems and processes.

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