Chapter 3

# P temperaturedependenceofthegibbsfreeenergy

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Unformatted text preview: therefore no disorder.  Marand’s Notes: Chapter 3 ‐ The Second Law of Thermodynamics  116    Helmholtz and Gibbs Free Energies  We have discussed at some length the Second Law of Thermodynamics,  which provides criteria for spontaneity and reversibility applicable to any  processes.  ΔSUnivese = ΔS + ΔSSurr &gt; 0 for a spontaneous process and ΔSUniverse = 0for a  reversible process or for conditions of equilibrium.  Such criteria although  very useful are not extremely practical as they require us to carry out  calculations for both the system and the surroundings.  It would be  extremely advantageous to find criteria for spontaneity, which are based on  the use of thermodynamic state functions for the system and which do not  invoke the surroundings. This can be done under the specific conditions  (constant volume and temperature or constant pressure and temperature),  which are encountered in many processes in chemical, physical and  materials sciences.          Marand’s Notes: Chapter 3 ‐ The Second Law of Thermodynamics  117  Helmholtz Free Energy:   Let us assume we are dealing with a process occurring at constant volume.   The heat exchanged with the surroundings is equal to change in internal  energy.  dU = δqV  The second law, written in the form of the Clausius Inequality states:   dS &gt; δq / T  Note that this inequality comes from dS + dSSurr  &gt; 0 and dSSurr = ‐ δq / T  Therefore, we can rearrange this equation as δq ‐ T dS &lt; 0 since T is always  positive.  This leads in...
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