Dear Ranjan
In the absence of any friction, then the net entropy change is 0.
 
 For any real process, there is friction. Entropy is transferred with  heat transfer, and the direction of entropy transfer is the same as that  of heat transfer. So, any time heat is transferred into the system, the  entropy of the system increases. Any time heat is transferred out of  the system, the entropy of the system decreases. Heat transfer out is  the only means of decreasing system entropy of a closed system. For an  open system, entropy can be transferred out with energy transfer out,  and with mass transfer out. 
 
 so any real process increases the entropy of the system. But whether the  entropy of the system itself increases or decreases is dependent on the  heat transfer. 
 
 For an isolated system, there is no heat transfer, there is no means of  reducing the entropy of the system. Which means that for any real  process in an isolated system, the entropy of the system increases, and  the energy available to do work decreases.



All the best.                                                           
AKASH GOYAL
AskiitiansExpert-IIT Delhi
 
Please feel free to post as many doubts on our discussion forum as you can. We are all IITians and here to help you in your IIT JEE preparation.
Win exciting gifts by answering the questions on Discussion Forum. So help discuss any query on askiitians forum and become an Elite Expert League askiitian. 
Now you score 5+15 POINTS by uploading your Pic and Downloading the Askiitians Toolbar  respectively : Click here to download the toolbar..