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CH%20301%20Chapter%207%20notesv2 - CH301 Chapter 7: A crash...

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CH301 Chapter 7: A crash course in entropy, free energy and the 2 nd and 3 rd laws of TM: The Second Law of Thermodynamics In spontaneous changes the universe tends towards a state of greater entropy .” A mirror shatters when dropped - does not reform. Its easy to scramble an egg - impossible to reverse! Food dye when dropped into water disperses Spontaneous processes are those which occur by themselves . Think of a spontaneous process as being ‘feasable’. Spontaneity has nothing to do with speed . What is Entropy? Entropy (S) is disorder, but on a molecular level. A jumbled sock drawer is a metaphor for disorder! thermal disorder: Add heat energy to a sample: molecules can occupy a more varied combination of translational, vibrational and rotational energy levels. positional disorder: Allow a sample to expand or mix with another material: molecules can occupy more physical locations. Quantitative definition of Entropy Entropy is a state function, so S is path independent. When heat, q, is transferred into a system reversibly* at constant temperature: S = q rev / T Units of S are J/K (for a specific amount) or, J/mol.K If S > 0 disorder increases If S < 0 disorder decreases *ie done slowly: surroundings stay at almost the same temperature Boltzmann: Entropy on a Molecular level microstate : exact translational, vibrational, rotational, potential energies of each particle in a system. macrostate: overall SUM of these energies Number of possible microstates (to form a given macrostate) = W. Add energy, and W increases. S = k lnW if W = 1 then S = 0 Entropy Changes in Changes of State Two possibilities: melting (fusion) or boiling (vaporization) Use S = q rev / T and note q = H fus or H vap . T will be either the melting point or boiling point (in K): Boiling point is that determined at 1atm.
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CH%20301%20Chapter%207%20notesv2 - CH301 Chapter 7: A crash...

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