1. Thermodynamics vs. Kinetics
Domain of Kinetics
Rate of a reaction depends on the pathway from reactants to products.
Thermodynamics tells us whether a reaction is spontaneous based only on the properties of reactants and products.

2. Entropy (S) A measure of the randomness or disorder
The driving force for a spontaneous process is an increase in the entropy of the universe
Entropy is a thermodynamic function describing the number of arrangements that are available to a system
Nature proceeds toward the states that have the highest probabilities of existing

3. Positional Entropy
The probability of occurrence of a particular state depends on the number of ways (microstates) in which that arrangement can be achieved
Ssolid < Sliquid << Sgas

4. The Expansion of An Ideal Gas Into an Evacuated Bulb

5. The Microstates That Give a Particular Arrangement (State)

6. The Microstates That Give a Particular Arrangement (State)

7. Entropy is a Measure of Disorder
Generally, the more complex the molecule, the higher the standard entropy value.
Entropies of ionic solids become larger as the attractions among ions become weaker.
Entropy usually increases when a pure solid or pure liquid dissolves in a solvent.

8. Concept Check
Predict the sign of S for each of the following, and explain:
The evaporation of alcohol
The freezing of water
Compressing an ideal gas at constant temperature
Heating an ideal gas at constant pressure
Dissolving NaCl in water + –
a) + (a liquid is turning into a gas)
b) - (more order in a solid than a liquid)
c) - (the volume of the container is decreasing)
d) + (the volume of the container is increasing)
e) + (there is less order as the salt dissociates and spreads throughout the water)

9. Second Law of Thermodynamics
"In any spontaneous process there is always an increase in the entropy of the universe"
"The entropy of the universe is increasing"
For a given change to be spontaneous, Suniverse must be positive
Suniv = Ssys + Ssurr

10. Calculating Entropy Change in a Reaction (System)
Entropy is an extensive property (a function of the number of moles)

11. Calculating Entropy Change for Surroundings
∆Ssurr. =
qsurr.
- ∆Hsystem T

12. ΔSsurr
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13. ΔSsurr
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14. Interplay of Ssys and Ssurr in Determining the Sign of Suniv