1.

A certain mass of an ideal gas is expanded from (1L, 10 bar) to (4L,5bar) against a constant external pressure of 1 bar. If initial temperature of gas is 300 K and the heat capacity of process is 50J//""^(@)C. Then the enthalpy change during the process is :

Answer»

`DeltaH=14.7 KJ`
`DeltaH=15.7 KJ`
`DeltaH=14KJ`
`DeltaH=0`

Solution :(B) (1L, 10bar ) to (4L, 5 BAR )
`(P_(1)V_(1))/(T_(1))=(P_(2)V_(2))/(T_(2))implies(10xx1)/(300)=(5xx4)/(T_(2))`
`implies T_(2)=600K`
`Q=CDeltaT=50xx[600-300]=15000` Joule=15kJ
`W=-P_("EXT")[V_(2)-V_(1)]`
`=-1[4L-1L]=-`3BAR litre=-0.3 kJ
`Delta=Q+W`
`=15-0.3=14.7kJ`
`Delta=DeltaU+(P_(2)V_(2)-P_(1)V_(1))`
`=[14.7+(5xx4-10xx1)/(10)]kJ=15.7`


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