If heat is supplied to an ideal gas in an isothermal process.

Explanation

Suppose the sample contains n moles. Also,
suppose the volume changes from `V^(1) to V^(2)` and the
temperature changes from `T^(1) to T^(2)`.
The heat supplied is
`DeltaQ = nCp(T^(2) -T^(1))`.
(a) The change in internal energy is `DeltaU = nCv (T^(2) - T^(1)) = Cv / Cp nCP (T^(2) - T^(1))`
`= Cv / Cp DeltaQ = 140 J / 1.4 = 100 J`.
(b) The work done by the gas is
`DeltaW = DeltaQ - DeltaU
140 J - 100 J = 40 J`.