1. Presented by Katie Hall
Spontaneous and Nonspontaneous Processes- Entropy and Second Law of Thermodynamics
Presented by Katie Hall

2. 95 watts dissipated as heat
Nature’s Heat Tax
5 Watts emitted as light
First Law of Thermodynamics: Energy cannot be created or destroyed SO energy cannot be greater at the end of an energy transfer
During every transfer of energy, heat is lost to the surroundings
Impossibility of perpetual motion machines
Most energy transfers don’t even run to maximum efficiency
95 watts dissipated as heat
100 Watts of electrical energy

3. Spontaneous and Nonspontaneous Processes

4. Spontaneous and Nonspontaneous Processes
A spontaneous process is one that occurs without ongoing outside intervention.
Spontaneity of a chemical reaction ≠ Speed of a reaction
Spontaneity=the direction in which and extent to which a chemical reaction proceeds
Speed=how fast a reaction takes place
Catalysts can speed up spontaneous reactions but can not make nonspontaneous reactions spontaneous

5. Spontaneous and Nonspontaneous Processes

6. Spontaneous and Nonspontaneous Processes

7. Spontaneous and Nonspontaneous Processes
A nonspontaneous process is not impossible.
It can be made spontaneous by coupling it to another process that is spontaneous OR by supplying energy from an external source.

8. Entropy and the Second Law of Thermodynamics

9. Second Law of Thermodynamics
For any spontaneous process, the entropy of the universe increases (ΔSuniverse > 0)
Processes that increase the entropy of the universe occur spontaneously.

10. Enthalpy and Spontaneity
Reactions that start with more potential energy than they end with (exothermic reactions) are often spontaneous
Endothermic reactions can also be spontaneous due to entropy.

11. What is Entropy?

12. What is Entropy?
A measure of the energy randomization or energy dispersal in a system.

13. What is Entropy?
A measure of the energy randomization or energy dispersal in a system.
But more specifically...

14. In spontaneous reactions, disorder or randomness (entropy) increases.
“Entropy (S) is a thermodynamic function that increases with the number of energetically equivalent ways to arrange the components of a system to achieve a particular state.” (pg. 818)
S=k lnW
k=constant (gas constant divided by Avogadro’s number)=1.38 x 10^-23 J/K
W=number of energetically equivalent ways to arrange the components of the system; in other words, number of possible microstates in a macrostate
In spontaneous reactions, disorder or randomness (entropy) increases.

15. System B (second microstate)
Entropy
System B (second microstate)
System A
System B
E=3J
E=3J
Energy
E=2J
Energy
Energy
E=1J
E=1J

16. System B (second microstate)
Entropy
System B (second microstate)
System A
System B
E=3J
E=3J
Energy
E=2J
Energy
Energy
E=1J
E=1J
W=1
W=2

17. Entropy
System B has more energetically equivalent ways to arrange the system so it has greater entropy.
So the state with the highest entropy also has the highest dispersal of energy.
“A state in which a given amount of energy is more highly dispersed (or more highly randomized) has more entropy than a state in which the same energy is more concentrated” (pg.820)

18. Entropy
This idea expands as we begin to look at things with more particles…
Here two containers are connected with a chamber. One container has gas inside and when the chamber is opened the gas is allowed to disperse.
States A-C are different possibilities for the dispersal of the gas particles (only four for this example)

19. Entropy States A and B only have one microstate (one possibility)
State C has 6 different microstates so it has a greater W value and therefore a greater entropy

20. Entropy ΔS=Sfinal-Sinitial
As the number of atoms increases the number of microstates that lead equal numbers of atoms in both flasks increases much more than the number of microstates of all atoms in one flask which remains 1
More microstates=More entropy
The more atoms there are the higher the probability that the gas will equally disperse between the two flasks
ΔS=Sfinal-Sinitial

21. Practice Problem

22. Practice Problem
Positive
Negative
Positive

23. Second Law of Thermodynamics
For any spontaneous process, the entropy of the universe increases (ΔSuniverse > 0)
Processes that increase the entropy of the universe (result in more disorder) occur spontaneously.
Ted-Ed:

24. The Entropy Change Associated with a Change in State

25. Entropy Change Associated with a Change in State
Gases have more ways to have the same energy of particles
More straight-line motions
Solids have less possibilities
They vibrate
Gases have the most entropy
Solids have the least entropy

26. Entropy Change Associated with a Change in State
Entropy increases for the following:
Phase transition from solid to liquid
Phase transition from solid to gas
Phase transition from liquid to gas
An increase in number of moles of a gas during a chemical reaction

27. Sources for Images-(In order of appearance)