the following pics are taken from resnick halliday fundamentals of physics.They clearly say that the entropy change of the system for an irreversible process between two equilibrium states i and f (say) will be same as that for a reversible process between the same two states.This is because entropy being state function depends only on the initial and final states...and for convenience we write it as equal to that for the reversible process..asdSsystem = [i ][f ] (dQr / T)........where dQr is the heat taken by the system in the reversible process.Now they again say that total entropychangeof system and surrounding for a reversible process will be zero and that for an irreversible process willbegreater than zero.The first part is clear...if in a reversible process system absorbs heat dQr ,then surrounding also loses the same heat .So dSsurrounding for reversible process = - [i ][f ] (dQr / T)So dSuniverse(reversible process)= dSsystem+ dSsurrounding = [i ][f ] (dQr / T) - [i ][f ] (dQr / T) = 0Now how should i define dSsurrounding(for irreversible process) such thatdSuniverse(irreversible process) = dSsystem+ dSsurrounding> 0__________________________________________________________________It is to be noted that dSsystem = [i ][f ] (dQr / T) for both reversible and irreversibleprocess as entropy of the system is a state function and does not depend onthe path followed (read the passages)__________________________________________________________________
Kevin Nash , 11 Years ago
Grade upto college level