Question

The statement that is incorrect among the following is:

• A. For an isothermal process, work done in reversible expansion is more than work done in irreversible expansion
• B. For an isothermal irreversible expansion, greater the difference in initial and final pressure, lesser is the work done
  
• C. For an isothermal irreversible compression, greater the difference in initial and final pressure, greater is the work done
• D. None of the above

Answer 1

The correct option is D None of the above

We know,
$W=-P_{ext}(V_f-V_i)$
For an expansion work.
$P_{ext}=P_{initial}-dP$

For a reversible expansion process, dP tends to zero, hence
$P_{initial}=P_{ext}$
For an irreversible process dP has a finite value and $P_{ext}$ is lesser than $P_{initial}$
greater the $P_{ext}$ greater is the work done. Hence the work done in reversible expansion is greater than irreversible expansion.
Between the two irreversible processes, one with lesser dP has a greater work.

For a compression work,
$P_{ext}=P_{initial}+dP$
For a reversible expansion process, dP tends to zero, hence
$P_{initial}=P_{ext}$
For an irreversible process dP has a finite value and $P_{ext}$ is greater than $P_{initial}$

Greater the $P_{ext}$ greater is the work done. Hence the work done in irreversible compression is greater than reversible compression.