1. Entropy changes in irreversible Processes To obtain the change in entropy in an irreversible process we have to calculate DS along a reversible path between the initial state and the final state. Freezing of water below its freezing point Irrev H2O( l , -10 °C) H2O( s , -10 °C) H2O( s , 0 °C) H2O( l , 0°C)

2. Absolute entropy of a substance Third law of thermodynamics: The entropy of each pure element or substance in a perfectly crystalline form is zero at absolute zero.

3. Spontaneous process

5. Helmholtz free energy

6. Gibb’s Free Energy

7. Combining the First and Second law

9. The Thermodynamic Square H S P U G T V A

10. H S P U G T V A

11. The variation of Gibb’s energy with temperature.

12. Variation of the Gibb’s energy with pressure

13. Conditions for equilibrium between Phases  

15. Various Equilibrium conditions

16.  

17. Phase changes of pure component

18. Temperature dependence of phase stability

19. Response of melting temperature to the applied pressure