February 09, 2025, 06:53:57 PM
Forum Rules: Read This Before Posting


Topic: Temp. Change in adiabatic process  (Read 953 times)

0 Members and 3 Guests are viewing this topic.

Offline Hunter2002

  • Very New Member
  • *
  • Posts: 1
  • Mole Snacks: +0/-0
Temp. Change in adiabatic process
« on: January 18, 2025, 09:24:01 AM »
I'm revising my notes, and it says that when the number of equilibrium steps increases in moving from one state to another, the area under pv curve and hence the magnitude of work done increases.
In regards to this the magnitude of work done by a reversible process is greater than an irreversible process.
Now in adiabatic compression of an ideal gas, W=∆U and work done is positive. According to my teacher, under reversible adiabatic compression, the final temperature of gas will be less than the final temperature in case of irreversible adiabatic compression.
Shouldn't it be the other way round?
Since more positive work will be done by the reversible heating, resulting in a larger positive change in U which is only a function of temperature?

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 2075
  • Mole Snacks: +302/-12
Re: Temp. Change in adiabatic process
« Reply #1 on: January 19, 2025, 04:52:55 PM »
I'm not sure your first sentence is true, or even meaningful.

The work done on the gas is greater for an irreversible than a reversible process. BUT:
For expansion, the magnitude of the reversible work is greater, but the sign is negative, so reversible expansion cools the gas more.
For compression. the magnitude of the reversible work is lower, but the sign is positive, so irreversible compression heats the gas more.
Either way, the final temperature is higher for the irreversible process (for the same final pressure). Your teacher is right.

Consider. The work done is -∫pextdV. For a reversible process, pext = pgas throughout. For an irreversible compression, pext > pgas (most simply, pext = pf throughout). So the magnitude of the work will be greater for an irreversible compression; contrariwise for an irreversible expansion.

Sponsored Links