# Difference between p-v and pressure and specific volume

what is the difference between pressure-volume and pressure-specific volume curves? since volume is an extensive property why do we plot pressure and volume curves for different processes?

Insofar as using specific volume $v$ or total volume $V$ is concerned, you can use either. However, for a closed system the mass is constant (e.g., ideal gas in cylinder/piston). Since the mass is fixed (and can be obtained by ideal gas law), you normally use total volume $V$ to find total work done by/on the mass. For open systems where the mass flow rate may be a variable, you would use the specific volume (volume per unit mass) to compute the work done per unit mass. Multiplying the work done per unit mass that by the mass flow rate will give you the rate of doing work (power).