Mole of the gas in the first compartment
n1=P1V1RT1=5×106×225/3×400=3000
Mole of the gas in the second compartment
n2=50×106×125/3×500=12000
The tank is rigid and insulated hence w=0
and q=0 therefore ΔU=0
Let Tf and Pf denote the final temperature and pressure respectively ΔU=n1Cv,m[Tf−T1]+n2Cv,m[Tf−T2]
=0
3000 (Tf−400)+12000(Tf−500)=0
Tf=480 K