ch302 notes ch 16 and 10

ch302 notes ch 16 and 10 - CH302 Chapter 10 Review and More...

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CH302: Chapter 10 Review.. and More.. The Second Law of Thermodynamics In spontaneous changes the universe tends towards a state of greater entropy .” Spontaneous processes occur by themselves. Spontaneity = ‘feasable’ i.e, has nothing to do with speed . What is Entropy? Entropy (S) is disorder, but on a molecular level . thermal disorder: add heat energy: molecules can occupy a more varied combination of translational, vibrational and rotational energy levels. positional disorder: expansion or mixing molecules can occupy more physical locations. In general, S solid <S liquid <S gas with solutions somewhere between liquid and gas. Can use this to qualitatively analyze a chemical reaction or physical process to predict the sign of Δ S. Expansion Work against CHANGING External Pressure FOR A REVERSIBLE, ISOTHERMAL expansion: Gradually reduce P ext from P initial to P final but keep system at constant T (e.g., water bath) since P = (nRT) / V: Substitute into w = - P ex Δ V d w = - (nRT/V) dV Integrate over all values of V (V 1 to V 2 ) : w = - nRT ln (V 2 / V 1 ) REVERSIBLE vs. IRREVERSIBLE Reversible : w = - nRT ln(V 2 /V 1 )