Enthalpy (H), Entropy (S), and Gibbs Free Energy (G)
Part 1 Screen Cast: http://www.youtube.com/watch?v=XcpsN5nOkKQ&feature=youtu.be
Note Packets: 1. Intro - basic terms, first law, ENTROPY, second law
2. System and Surroundings
3. Entropy in Chem Rxns
4. G, Free Energy
5. G and w
6. G and Chem Rxns
Powerpoint Referenced in Class Lecture (begin with slide #44)
Sample Free Response
Sample Multiple Choice
2009 Free Response - Question & KEY
A process is spontaneous if it occurs without outside intervention (a cup of hot coffee cools, iron rusts, etc.). What determine spontaneity is 1) enthalpy (is the process lowering the energy of the system) and/or 2) entropy (is the process increasing the disorder of the system).
ENTROPY is "randomness," "disorder," "degree of freedom."
Positional Probability is the probability that depends upon the number of possible arrangements. A processes may be spontaneous if it increases the positional probability of the system.
THERMODYNAMICS VIDEO #1: Chpt Into and ENTROPY (S)
Crash Course Video - ENTROPY
THERMODYNAMICS VIDEO #2: Entropy Changes in Chem Rxns
Gibbs Free Energy and Equilibrium
First . . . the difference between "Delta G" and "Delta G knot:"
It is very important to be aware of this distinction; that little ° symbol makes a difference! First, the standard free energy change ΔG° has a single value for a particular reaction at a given temperature and pressure; this is the difference
(ΣG°f, products – ΣG°f, reactants) that you get from tables. It corresponds to the free energy change for a process that never really happens: the complete transformation of pure N2O4 into pure NO2 at a constant pressure of 1 atm.
The other quantity ΔG, defined by ΔG = ΔG° + RT ln Q, represents the total free energies of all substances in the reaction mixture at any particular system composition. (http://www.chem1.com/acad/webtext/thermeq/TE5.html)
The free energy G is a quantity that becomes more negative during the course of any natural process. Thus as a chemical reaction takes place, G only falls and will never become more positive. Eventually a point is reached where any further transformation of reactants into products would cause G to increase. At this point G is at a minimum (see the plot below), and no further net change can take place; the reaction is at equilibrium.
N2O4(g) → 2 NO2(g)
The free energy of 1 mole of N2O4 (1) is smaller than that of 2 moles of NO2 (2) by 5.3 kJ; thus ΔG° = +5.3 kJ for the complete transformation of reactants into products. The red curved line show the free energy of the actual reaction mixture. This passes through a minimum at (3)where 0.814 mol of N2O4 are in equilibrium with 0.372 mol of NO2. The difference (4)corresponds to the free energy of mixing of reactants and products which always results in an equilibrium mixture whose free energy is lower than that of either pure reactants or pure products. Thus some amount of reaction will occur even if ΔG° for the process is positive.
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