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Chapter 17.1-17.4

CHEM 1A Chapter Notes - Chapter 17.1-17.4: Gas Constant, Avogadro Constant, Spontaneous Process


Department
Chemistry
Course Code
CHEM 1A
Professor
Arnold Yuan
Chapter
17.1-17.4

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Lecture 26: What a Mess
PRE-READING NOTES
17.1-17.4 pg. 769-784
17.1 Nature’s Heat Tax: You Can’t Win and You Can’t Break Even
first law of thermodynamics – energy is conserved
second law of thermodynamics – cannot win and cannot break even in an energy
transaction
heat tax
cannot achieve maximum efficiency – some energy is lost to surroundings
17.2 Spontaneous and Nonspontaneous Processes
spontaneous process – one that occurs without ongoing outside intervention
system tends toward lowest potential energy
- definition of lowest potential energy?
spontaneity different from speed
nonspontaneous reaction can be made spontaneous by coupling with a very spontaneous
reaction
17.3 Entropy and the Second Law of Thermodynamics
can’t just look at exothermic/endothermic
- endothermic and entropy increases  spontaneous
entropy (S) – thermodynamic function that increases with the number of
energetically equivalent ways to arrange the components of a system to achieve a
particular state
S = k ln W, where k is Boltzmann constant (gas constant/Avogadro’s number), W is # of
energetically equivalent ways to arrange components of a system
W – all microstates that can result in a given macrostate
- a microstate is one distribution of energy among particles
- macrostate: P, V, T
- energy constantly redistributed
Highest entropy – also greatest dispersal of energy  more ways to arrange
Second law of thermodynamics For any spontaneous process, the entropy of the
universe increases (DSuniv > 0)
Entropy is state function, determines direction of chemical and physical change
(greater energy randomization – energy is dispersed)
entropy increases as solid to liquid to gas
gas – more ways to distribute its energy – straight-line motions of molecules, rotations of
molecules (translational and rotational energy)
17.4 Heat Transfer and Changes in the Entropy of the Surroundings
DSuniv > 0 = DSsys + DSsurr
exothermic reaction releases heat – increases entropy of surroundings
endothermic takes in heat from surroundings – decreases entropy of surroundings
magnitude of increase in entropy of the surroundings is temperature dependent
for water evaporating – increase in entropy of water is enough to overcome decrease in
entropy of surroundings (which is proportional to heat taken in)
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