Entropy and Equilibrium
- According to the Second Law of Thermodynamics, a change takes place in the direction which corresponds to an increase in Stotal.
- This is the case for the freezing of water below temperatures of 0oC; however, above this temperature the Stotal for the freezing of ice is negative and so the reverse occurs; the ice melts.
- When the Stotal is zero, there will be no tendency for the reaction to go in either direction; it will be at equilibrium.
- This can be shown once again for the freezing and melting of water:
- At 273K, the Stotal for the equilibrium reaction is:
- The reaction is at equilibrium; liquid water and ice exist together at 0oC.
At equilibrium, the Stotal is equal to zero.
- Even though theoretically the equilibrium occurs at 0oC, the temperature does not have to be exactly equal to this for it to occur.
- If the conditions happen to be standard, then the standard entropy change will be zero; however, the change rarely is zero at equilibrium.
Useful books for revision
Revise A2 Chemistry for Salters (OCR A Level Chemistry B)
Salters (OCR) Revise A2 Chemistry