A gas `(C_(v.m) = (5)/(2)R)` behaving ideally is allowed to expand reversibly and adiabatically from `1` litre to `32` litre. Its initial temperature is `327^(@)C`. The molar enthalpy change (in `J//mol`) for the process is :

Options

A. `-1125R`
B. `-675`
C. `-1575R`
D. None of these

Answer

C

Explanation

`(T_(2))/(T_(1))=((V_(1))/(V_(2)))^(gamma-1)`
`T_(2)=T_(1).((1)/(32))^((7)/(5)-1)=600.((1)/(2^(5)))^((2)/(5))`
`=600(0.5)^(2)=150K`
`DeltaH_(m)=(7)/(2)Rxx(150-600)=-1575R`