A gas present in a cylinder fitted with a frictionless pistion expands against a constant pressure of `1atm` form a volume of `2L` to a volume of `6L`. In doing so, it absorbs `800J` heat form the surroundings. Determine the increases in internal enegry of process.

Answer

395

Explanation

Since, work is done against constant pressure and thus, irreversible.
Given, `DeltaV = (6-2) = 4L, P=1` atm
`therefore W=-1 xx 4 L- atm =(-1 xx 4 xx 1.987)/(0.0821)` cal
(since 0.0821 L atm = 1.987 cal)
`=-96.81 cal=-96.81 xx 4.184 J (therefore 1 "cal" = 4.184 J)`
`=-405.05` J
Now from 1st law of thermodynamics
`q= DeltaU -W`
`800 = DeltaU + 405.05`
`therefore DeltaU = 395 J`