36-entropy - Ch. 10 - Recap W h a t is e n tr o p y ? D eg...

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1 Week 15 CHEM 1310 - Sections L and M 1 Ch. 10 - Recap What is entropy? Degree of disorder of a system Equations for calculating entropy S = k B ln rigorous definition S = q reversible /T For melting: S = H fusion /T m For evaporation: S = H vap /T b S = nC p ln(T 2 /T 1 ) or S = nC V ln(T 2 /T 1 ) Week 15 CHEM 1310 - Sections L and M 2 Ch. 10 - Recap What is spontaneity? Likelihood that a reaction will proceed without outside influences Spontaneity has nothing to do with the speed of a reaction. Both entropy and Gibbs’ free energy terms help us to predict whether a reaction will proceed spontaneously or not. How?… Week 15 CHEM 1310 - Sections L and M 3 Ch. 10 - Recap Entropy as an indicator of reaction spontaneity 2 nd Law of Thermodynamics: in any spontaneous process there is an increase in the entropy of the universe. S universe = S system + S surroundings If S universe is positive , then the process is spontaneous . If S universe is negative , then the process is non-spontaneous . S universe is still to difficult to measure. Need a more practical indicator!
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2 Week 15 CHEM 1310 - Sections L and M 4 Ch. 10 - Recap Gibbs’ free energy as an indicator of reaction spontaneity Equation relates thermodynamics terms G = H - TS expressed in terms of the system G = H - T S How does G help us to predict rxn spontaneity? Week 15 CHEM 1310 - Sections L and M 5 Ch. 10 - Recap G = H - T S Divide both sides of the eqn by “-T” When G is negative , S univ is positive: spontaneous reaction
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36-entropy - Ch. 10 - Recap W h a t is e n tr o p y ? D eg...

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