1. Thermo – the 2 nd Law Two factors effect any process such as a chemical reaction. 1.the difference in any energy term, ΔE, ΔH or ΔS, between the reactants and products. That is between the final and initial states. 2.The pathway the process follows.

2. Thermo – the 2 nd Law Thermodynamics is the study of the energy of the initial and final states. Kinetics is the study of the pathway between these states.

3. Thermo – the 2 nd Law A Conundrum or two A ball spontaneously rolls downhill but never up. Water at a temperature below 0 o C freezes spontaneously, but above 0 o C ice melts. And the freezing of water is exothermic, while the melting is endothermic. So why are these spontaneous?

4. Thermo – the 2 nd Law There are obviously two different thermodynamic properties at play here. These are Enthalpy and an new one, Entropy. Entropy is a measure of the positional freedom of a set of particles.

5. Thermo – the 2 nd Law In any spontaneous process the entropy of the universe increases. Or You not only can’t win, you can’t break even.

6. Thermo – the 2 nd Law ΔS, the change in entropy, is a measure of the change in positional freedom of a set of particles. E.g. B&G spreads salt on the sidewalks. How does the entropy of the salt change as it dissolves? As the ice melts? As the water evaporates? As the salt recrystalizes?

7. Thermo – the 2 nd Law Gibbs Free Energy The maximum energy available for any thermodynamic process, G. G = H – TS & ΔG = ΔH – TΔS Note how ΔG changes as ΔH, goes from 0, as ΔS goes from 0 and as T changes.

8. Thermodynamics the Isothermal expansion of an ideal gas ΔT = 0, therefore ΔE = 0 and –q = w (or q = -w). If we let V change in infinitesimal steps we find, w = -  P external dV from V i to V f, or w = -nRT(lnV f -V i ) = -nRT*ln(V f /V i ) = -q

9. Thermodynamics the Adiabatic expansion of an ideal gas No heat may flow into or out of the system. q=0, ΔE = w = -PΔV  = C P and C P = 5/2R while C V =3/2R C V (for a monatomic gas) P i V i  =P f V f  we can use the ideal gas equation to find ΔT and, since ΔE = w = nC V ΔT, we can find the work.

10. Thermodynamics the Adiabatic expansion of an ideal gas IsothermalP i V i = P f V f or PV is constant AdiabaticP i V i  = P f V f  or PV  is constant