Free Energy

hippo_li.gif (2057 bytes)

    Free energy is symbolized by the letter G.  G can be defined as

                       wpe3.gif (856 bytes) G = wpe3.gif (856 bytes)H - Twpe3.gif (856 bytes)S

where H is enthalpy, T is the temperature in Kelvin, and S is the entropy.
    When a process is at a constant temperature, then the change of free energy (can be given in the equation

                 wpe3.gif (856 bytes)G = wpe3.gif (856 bytes)H - Twpe6.gif (856 bytes)S

This equation cwill tell us that a process is spontaneous when free energy is negative(-wpe7.gif (856 bytes)G).   When a process is at equilibrium, then wpe3.gif (856 bytes)G = 0.

wpe8.gif (856 bytes)S positve, wpe9.gif (856 bytes)H negative Spontneous at all temperatures
wpeB.gif (856 bytes)S positive, wpeA.gif (856 bytes)H positive Spontaneous at high temperatures ( where exothermicity is relatively unimportant)
wpeC.gif (856 bytes)S negative, wpe10.gif (856 bytes)H negative Spontanous at low temperatures (where exothermicity is dominant)
wpeF.gif (856 bytes)S negative, wpeE.gif (856 bytes)H positive Process no spontaeous at any tmperature (reverse process is spontaneous at all temperatures)

    

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