A chemist while studying the properties of gaseous `C_(2)Cl_(2)F_(2)`, a chlorofluoro carbon refrigerant, cooled a `1.25 g` sample at constant atmospheric pressure of `1.0 atm` from `320 K` to `290 K`. During cooling, the sample volume decreased from `274` to `248 mL`. Calculate `Delta H` and `Delta U` for the chlorofluoro carbon for this process. For `C_(2)Cl_(2)F_(2)`, `C_(P) = 80.7 J mol^(-1) K^(-1)`.

Explanation

Mass of chlorofluoro carbon `=1.25 g`
`Mw=133`
`C=80.7//133=0.606 J g^(-1)`
`DeltaT=(-320+290)=-30 K`
`DeltaH=mxxC_(P)xxDeltaT=1.25xx0.6060xx(-30)=-22.8 J`
`DeltaV=(248-274) mL=-26 mL=-0.026 L`
`P DeltaV=1xx-0.026`
`=-0.026 atm-L`
`=-0.026xx101.3=-2.6 J ( :' 1 atm-L =101.3 J)`
`DeltaU=DeltaH-p DeltaV=-22.8-(-2.6)=-20.2 J ( :' DeltaH=DeltaU+p DeltaU)`