Download Entropy Notes II

WARM UP
Think back to the our thermodynamics
unit. In any exothermic reaction, lots of
heat is created quickly, and the reaction
creates lots of entropy. What is
entropy?
The Big Bang Theory
Entropy
Chemistry II
Entropy (S)
• A measure of disorder/randomness
– More disorder, higher entropy
– Universe tends to move toward greater entropy
Entropy (S)
• Microstates (probable arrangements)
– Ludwig Boltzmann
– The more microstates, the higher the entropy
Second Law of Thermodynamics
• The entropy of the universe increases in a
spontaneous process
– Decreases in a non-spontaneous one
Entropy Calculations
• Standard entropy
– From known data – Appendix 3
– Δ Srxn = Sproducts – Sreactants
• Unit is J/K·mol
Entropy Calculations
• Entropy and Energy
– Δ Suniverse = Δ Srxn + -(Δ E)rxn
– Heat production increases entropy
Third Law of Thermodynamics
• The entropy of a perfect/pure crystalline solid
is zero at a temp of 0 K (absolute zero)
– Perfect order
Third Law of Thermodynamics
– Allows for standard entropy calculations
• Δ S = Sfinal – 0
WRAP UP
• Predict the entropy change for the following:
– Burning gas in your car
– Melting ice
– Locker clean-out day
WARM UP
• Define entropy.
• Explain the second law of thermodynamics.
Why does the universe work this way?
WRAP UP
1. Use the standard entropies to
calculate the standard entropy of:
H2(g) + ½ O2(g)  H2O(l).
(remember that you need to factor
stoichiometry into your equation)