A gas contained in a cylinder fitted with a frictionless piston expands against a constant external pressure or 1 atm from a volume of 5 litres to a volume of 10 litres. In doing so it absorbs 400 J of thermal energy from its surroundings. Determine the change in internal energy of system.

A gas contained in a cylinder fitted with a frictionless piston expand

1.	A gas contained in a cylinder fitted with a frictionless piston expands against a constant external pressure or 1 atm from a volume of 5 litres to a volume of 10 litres. In doing so it absorbs 400 J of thermal energy from its surroundings. Determine the change in internal energy of system.
Answer» Solution :Given DATA q = 400 J, `V_(1) = 5L , V_(2) = 10 L` `Delta U` = q - W (heat is given to the system (+q), work is done by the system (-w) `Delta u = q - Pd V ` = 400 J - 1 atm ( 10 - 5) L = 400 J - 5 atm L[`:'`1 L atm = 101 . 33 J ] = 400 J - ` 5 xx 101 . 33 ` J = 400 J - 506 65 J = - 106 . 65 J .