A piston-cylinder device initially contains 2 L of air at 100 kPa and 25 ℃. Air is now compressed to a final state of 600 kPa and 150 ℃. The useful work input is 1.2 kJ. Assuming the surroundings are at 100 kPa and 25 ℃, determine the minimum work that must be supplied to accomplish this compression process. (answer in kJ)

Explanation:

In order to determine the work done, we will first calculate the internal energy as follows.

                  =

                  = 0.171 kJ

Now, we know that relation between internal energy and pressure according to the first law of thermodynamics is as follows.

                = q + w

Since, in the given situation heat energy (q) is equal to 0. Therefore,

                    = w

                          = 0.171 kJ

Thus, we can conclude that minimum work that must be supplied to accomplish this compression process is 0.171 kJ.