Second Law of Thermodynamics , Reversible and Irreversible Processes

  • Second law of thermodynamics plank statement. It is impossible to construct a heat engine which can completely convert heat energy into mechanical energy without rejecting heat to surroundings.
  • Kelvin statement: It is impossible to extract work from a system by cooling it below surrounding temperature.
  • A process that can be retraced back in the opposite direction in such a way that the system passes through the same states as in the direct process and finally the system and surroundings return to their original status with no other change anywhere else is called a reversible process.
  • In reversible process the changes must take place at an infinitesimally slow rate and the system must always be in thermal and mechanical equilibrium with surroundings.
  • A process that can not be retraced back in the opposite direction is called an irreversible process.
  • The thermodynamic coordinate or parameter that gives the measure of disorder is called entropy. ds = dQ/T
  • In a reversible process entropy increases if heat is absorbed and vice versa

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