A sample of argon gas at `1atm` pressure and `27^(@)C` expands reversibly and adiabatically from `1.25 dm^(3)` to `2.50 dm^(3)`. Calculate the enthalpy change in this process. `C_(vm)` for orgon is `12.48J K^(-1) mol^(-1)`.

Explanation

Number of moles of argon present in the sample
`=(PV)/(RT)=(1.25xx1)/(0.0821xx300)=0.05075`
For adiabatic expansion,
`(T_(1))/(T_(2))=((V_(2))/(V_(1)))^(r-1)`
or `(300)/(T_(2))=((2.50)/(1.25))^(1.66-1)`
or `T_(2)=188.55K`
`C_P=C_(V)+R`
`=12.48+8.314`
`=20.794JK^(-1)" "mol^(-1)`
`DeltaH=nxxC_(P)xxDeltaT`
`=0.05075xx20.794xx(300-188.55)`
`=117.6J`