A gas has $T_{c} = 150 K$ . Assuming van der Waals behaviour, at which of the following temperatures will the gas both cool on Joule-Thomson expansion and show $Z$ greater than 1 at low pressure?

Answer: B

T_{B} = 27 T_{c} /8 = 506.2 K

and

T_{i} = 2 T_{B} = 1012.5 K

Z

greater than 1 at low pressure requires

T

above

T_{B}

; cooling on throttling requires

T

below

T_{i}

. Only

600 K

lies between

506 K

and

1013 K