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WHY does the 2nd law of Thermodynamics work?

  1. Mar 16, 2010 #1
    Dear All

    Can't get my head around this.

    Entropy of the universe (system+surroundings) always increases.
    But why?
    G = H - TS
    G = Energy available for work
    H = Enthalpy of reaction
    How can the energy available be greater than the enthalpy of the reaction?
    There must be some input from the 'rearrangement' of the molecules?
    Ok I can accept that.
    When S is positive for a chemical reaction there is more energy from the work than H dictates.
    How can it come from a a reaction becoming more disordered?
    This requires breaking bonds eg. Solid to liquid which REQUIRES energy. Logically more disordering reactions should be less spontaneous due to the additional energy required to break up the ordered molecules.

    Thereby making it more difficult to break things up than to put them together.
    Please Help
  2. jcsd
  3. Mar 17, 2010 #2
    Welcome Pjosheph.
    One must keep a 'tally' of the total energy & entropy properly. Consider what happens when you put a cube of ice on a hot pan -both kept inside a sealed box. Does the ice melt spontaneously? Also, does the entropy decrease as the volume decreases upto 4 C?
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