Question

1 mol of `NH_(3)` gas`( gamma = 1.33)` at `27^(@)C`is allowed to expand adiabatically so that the final volume becomes 8 times. Work done will be
A. 450 cal
B. 1800 cal
C. 900 cal
D. 300 cal

Answer 1

Correct Answer - C
Work done in adiabatic expansion` = - nC_(v) (T_(2) - T_(1))`. To calculate final tem. `T_(2)`, proceeding as in the above case, `T_(2) = 150 K`.
`C_(v)` for `NH_(3)= 3R`
`( NH_(3)` is a non-linear molecule with`N=4` .Hence, translational degrees`=3`, Rotational degrees`=3`. Total `U = ( 3)/(2) RT + (3)/(2)RT =3RT`)
`:. w=-1 xx3 xx2(150-300) = 900cal`