$3\mathrm{.}1$ Field work $($in a team$)$: Visit a CNG filling station. When a vehicle comes in for filling, touch the CNG cylinder. Repeat after the filling is complete. What do you notice? If you desire, take an IR temperature sensor and measure the cylinder exterior temperatures before and after filling.

$($a$)$ Consider the internal space of the CNG cylinder as the CV$.$ Write the conservation of mass and $1$st law equations for the filling process.

$($b$)$ Write the $2$nd law equation for this process.

$($c$)$ Why is this process irreversible?