A sample of ideal gas `(gamma = 1.4)` is heated at constant pressure. If an amount `140 J` of heat is supplied to the gas, find (a) the changes in internal energy of the gas, (b) the work done by the gas.

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
`Delta Q =Delta U + P Delta V= Delta U + n R Delta T = Delta U + (2 Delta U)/(f)`
(a) The change is internal energy is
`Delta U = n f /2 R (T_(2) -T_(1)) = f/2 R n (T_(2) -T_(1))`
`= (f) /(2+f) Delta Q = (140J )/(1.4) =100J`
(b) The work done by the gas is
`Delta W = Delta Q -Delta U =140J -100J =40J`