Derive Gibbs Energy change and non mechanical work.

Gibbs free energy is that thermodyanamic quantity of a system is whose value during a process is equal to the maximum possible useful work that can be obtained from the system.

,   q=∆U+wexpansion + wnon-expansion  …1

Under constant pressure condition 

,  q=∆U +P∆V +wnon-expansion =∆H + wnon-expansion ……2

For reversible change taking place at constant tempreture

  ∆S=qrev/T  or  qrev=T∆S  ……3

From 2 & 3

  T∆S=∆H + wnon-expansion  or ∆H-T∆S=-wnon-expansion

Under constant tempreture and pressure,

   ∆G=∆H-T∆S

At the end,

  ∆G=-wnon-expansion = non mechanical work (maximum)

 

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