Gas in a syringe being compressed - thermodynamic processes

[domingoleung]

Homework Statement

1. When the gas in a syringe was quickly compressed for 10s, pressure and temperature increased initially. Finally, pressure and temperature decreased. When the gas was naturally released, the pressure and temperature decreased initally. Finally, the temperature increased. What thermodynamic processes were gone through by the system?

2. Explain briefly why the final pressure cannot return to the inital atmospheric pressure

Relevant Equations

PV=nRT

1.
Adiabatic compression (When compressed quickly, there is no heat flow to the environment Q=0)
Isochoric with heat loss (The syringe is still compressed, there should be no change in volume)
Adiabatic expansion (When the syringe is released, there is work done only)
Isochoric with heat gain (The syringe is released entirely, there should be no change in volume)2.
Still I have no idea :(

 

[Chestermiller]

What does naturally released mean?

When the syringe reaches thermal equilibrium with the surroundings, its volume is larger, right, and its temperature is back to the starting value?