Tuesday, June 17, 2014

thermodynamics - Entropy Change in an irreversible process


I have just started learning thermodynamics and the concept of entropy confuses me.


Suppose I have a gas in a cylindrical container fitted with a piston. I take it through an adiabatic irreversible process to an other state. There is certainly some entropy change. But when I take it through an adiabatic reversible process to the same state as I did in the irreversible process, then the entropy change would be zero, because $Q_\text{reversible}$ in this case is zero. Now since entropy is a state function, $\Delta S$ should be the same in the two cases, but it is not.


Where am I going wrong?




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