Question

A gas contained in a cylinder fitted with a frictionless piston expands against a constant external pressure of 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 1

\(\triangle V =10-5=5 \space litre=5×10^3 m^3\)

\(Q=400J \space ,\space \space P=1atm =1.013×10^{-5} pa\) W=p.dV=\(1.013×10^5 ×5 ×10^{-3}\)

=506.5 J  

\(\triangle U=Q-W\) =400-506.5 J 

=-106.5 J 

\(|\triangle U|=106.5 J\)