FREE ENERGY        ΔG      =       ΔH        -     T ΔS
                                                   free energy     enthalpy       entropy

 

  ΔG is a numerical measure of how far a reaction is from equilibrium

  ΔG is measure amount energy in system able to do work (to stay away from equilibrium)...

                          Disorder increases (thus entropy increases) when useful energy,

                                   that which could be used to do work, is dissipated as heat........

 

                    most Cells are ISOTHERMAL  -  (4^o   to @  45^o )  - thus ΔH = 0

                            (function with a very narrow temp range)

                             thus, ΔG can PREDICT..... the Direction of Cellular Reactions......
                                      TOWARD EQUILIBRIUM  and  Maximum ENTROPY

 

 

 

 

 

 

 

 

 

 

 

 
 CHEMICAL REACTION    A <---> B     Which Way?
          
                                                                                 J. Willard Gibbs (1839-1903)
                   ΔG  = ΔG0’  +  R T ln [ p]/[ r]
  
    change in free energy content of a reaction...depends upon:
        1.  energy is stored in molecule's covalent bonds
        2. remember, temperature is negligible... cells are isothermal, i.e.,                      
                  ΔdG        =    actual free energy
                    ΔGo'       =    standard free energy [change under std conditions]
                      R           =    gas constant ( 2 x 10^-3 Kc/mol)
                      T           =    absolute temp (-273^oK)
                      ln          =    natural log (conversion log₁₀ = 2.303)

              at equilibrium   ΔG = 0     and    [p]/[r] = Keq
              if we solve above equation for ΔG0'  we can see teh relationship of Keq to ΔG0’
                                mallery's version of relationship*        (table 3.1 pg 98)

                                                                   

 

 

 

 

 
   CHEMICAL REACTIONS    A <----> B    Which way & Why?

    EXERGONIC REACTION - is one which releases free energy
        Product  [B]   <<< energy     REACTANT   [A]    [stored in covalent bonds]
            ex:    burning wood (cellulose)
                               glucose monomers  =  potential energy
                               breaks bonds, release heat & light ---> CO₂ & H₂O

                     cell respiration -  (heterotrophy) -  cellular burning of glucose
                               slower,   multi-step process to capture & release
                                            energy.... as ATP

    ENDERGONIC REACTION -   requires input of energy for   A --> B
        PRODUCT   [B]   >>>energy     Reactant   [A]
            ex:      photosynthesis -  (autotrophy)
                               glucose made from CO₂ + H₂O  --light--->   C₆H₁₂O₆
                                                           energy poor       vs.              energy rich
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