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

Let the sample of gas contain `n` moles.
At constant pressure, let the state of the gas change from `(V_(1),T_(1)) "to" (V_(2),T_(2))`
Heat supplied `dQ= n C_(p)(T_(2)-T_(1))= 140J`
Change in internal energy of gas
`dU= n C_(v) (T_(2)-T_(1)) = dU = n C_(v) (T_(2)-T_(1))= (nC_(v))/(C_(p)) C_(p) (T_(2)-T_(1))=(C_(v))/(C_(p))dQ=(140)/(1.4)= 100J ( :. gamma= (C_(p))/(C_(v))=1.4)`
Work done by the gas, `dW=dQ-dU=140-100= 40J`.