Consider several flow processes with ideal gases: 

(1) Compression of a gas mixture from 100 kPa to 200 kPa; 

(2) Cooling a gas mixture from 50◦C to ambient 20◦C using ambient air; 

(3) Mixing two different gases at 100 kPa; 

(4) Throttling a gas mixture from 125 kPa to 100 kPa. For each case, explain what happens to the exergy, whether there is any exergy destruction, and whether the composition is needed.