Question

In thermodynamics, the $P-V$ work done is given by $w=-\int d V P_{ ext }$
For a system undergoing a particular process, the work done is,
$w=-\int d V\left(\frac{R T}{V-b}-\frac{a}{V^{2}}\right)$
This equation is applicable to a

• A. System that satisfies the van der Waals equation of state
• B. Process that is reversible and isothermal
• C. Process that is reversible and adiabatic
• D. Process that is irreversible and at constant pressure

Answer 1

Answer: (A), (B), (C)

The following expression of $P - V$ work done
$W=-\int P_{\text {ext }} d V$
is applicable for reversible isobaric as well as isothermal and adiabatic process. If $P_{\text {/ext }}$ is substituted for a Vander Waals equation then it becomes
$W=-\int\left(\frac{R T}{V-b}-\frac{a}{V^{2}}\right) d V$
But it is not applicable for irreversible process which are carried out very fast. So work done is calculated assuming final pressure remains constant throughout the process