Answer
a) $P_2=159.26\ kPa$
b) $Q=-674.12\ kJ$
Work Step by Step
For an ideal gas :
$PV=mRT$
With $P_1=250\ kPa, T_1=550\ K, V_1=V_2=3\ m³,\ R=4.1240\ kJ/kg.K$:
$m=0.331\ kg$
The final pressure (with $T_2=350\ K)$:
$P_2=159.26\ kPa$
For a constant-volume process:
$Q=\Delta U = mc_v\Delta T$
With $c_v = 10.183\ kJ/kg.K$
$Q=-674.12\ kJ$
