1. PHYS 213 Midterm Exam HKN Review Session
Steven Kolaczkowski
Alex Littlefield

2. First Law of Life
Check your units

3. First Law of Thermodynamics
Check Your Units
d𝑈=𝑑𝑄+𝑑 𝑊 𝑜𝑛 =dQ−P𝑑𝑉
If volume is constant: d𝑈=𝑑𝑄

4. Entropy, Temperature, and the Second Law of Thermodynamics
CHECK YOUR UNITS
𝑆≡ 𝑘 𝐵 ln⁡(Ω) where Ω is the number of microstates
Ω 𝑡𝑜𝑡𝑎𝑙 = Ω 1 ∗ Ω 2 ∴ 𝑆 𝑡𝑜𝑡𝑎𝑙 = 𝑆 1 + 𝑆 2
𝑑𝑆= 1 𝑇 𝑑𝑈+ 𝑃 𝑇 𝑑𝑉− 𝜇 𝑇 𝑑𝑁
For an Isolated system Δ𝑆≥0 or Δ 𝑆 𝑈𝑛𝑖𝑣𝑒𝑟𝑠𝑒 ≥0
If Δ𝑆=0 the process is reversible
Temperature: 1 𝑇 ≡ 𝑑𝑆 𝑑𝑈 𝑉,𝑁

5. Equilibrium and Counting Microstates
We will observe the macrostate with the most microstates (maximum entropy)
A microstate is an observable state
Distinguishable: Ω= 𝑀 𝑁 Indistinguishable: Ω= 𝑀 𝑁 𝑁!
𝑆 𝑡𝑜𝑡𝑎𝑙 is maximized when T is constant across system (thermal equilibrium)

6. Heat Capacity and Latent Heat
Heat capacity: the amount of energy required to raise the temperature of a material by 1K
𝐶 𝑉 = 𝑑𝑄 𝑑𝑇 = 𝐽 𝐾
𝑐 𝑣 𝑚𝑜𝑙 = 1 𝑛 d𝑄 d𝑇 = 𝐽 𝑚𝑜𝑙∙𝐾 𝑐 𝑣 𝑚𝑎𝑠𝑠 = 1 𝑚 𝑑𝑄 𝑑𝑇 = 𝐽 𝑘𝑔∙𝐾
𝐶 𝑣,𝑡𝑜𝑡 = 𝐶 𝑣,1 + 𝐶 𝑣,2
𝑑𝑄= 𝐶 𝑣 ∙d𝑇=𝑚 𝑐 𝑣 𝑚𝑎𝑠𝑠 ∙𝑑𝑇 = 𝐽
Latent Heat: The amount of energy needed to transition between states of matter
T does not change during a phase change!
𝐿 𝑓 = Δ 𝑄 𝑠𝑜𝑙𝑖𝑑→𝑙𝑖𝑞𝑢𝑖𝑑 𝑚 𝑠𝑜𝑙𝑖𝑑 = 𝐽 𝑘𝑔 𝐿 𝑣 = Δ 𝑄 𝑙𝑖𝑞𝑢𝑖𝑑→𝑔𝑎𝑠 𝑚 𝑙𝑖𝑞𝑢𝑖𝑑 = 𝐽 𝑘𝑔

7. Ideal Gases and Equipartition
CHECK YOUR UNITS
Equipartition: The idea that thermal energy on average is distributed equally among all quadratic modes of motion
<𝐾>= 𝑘 𝐵 𝑇 2 for each quadratic degree of freedom
Monoatomic Gases: Diatomic Gases: Solids: 6
Mass doesn’t matter for calculating energy, but it does for finding average velocity
Ideal Gas Law: Assuming that particles will not collide or interact with each other, only with the walls of the container, and are volumeless
Works best with low densities and high temperatures (a few, fast moving particles)
𝑃𝑉= 2 3 𝑁<𝐾 > 𝑡𝑟𝑎𝑛𝑠 =𝑁𝑘𝑇=𝑛𝑅𝑇

8. Solids, More Heat Capacities, and Internal Energy
CHECK YOUR UNITS
𝑈=𝑁<K>
Ideal Solids
𝑈 𝑡𝑜𝑡𝑎𝑙 =𝑁 < 1 2 𝑚 𝑣 2 > 𝑡𝑟𝑎𝑛𝑠 +< 1 2 𝑘 𝑟 2 > =2𝑁<𝐾 > 𝑡𝑟𝑎𝑛𝑠 =3𝑁 𝑘 𝐵 𝑇
We will assume that ideal solids are incompressible 𝑑𝑈=𝑑𝑄 and 𝑐 𝑚𝑜𝑙 = 1 𝑛 𝑑𝑈 𝑑𝑇 =3 N A k B

9. Boltzmann Distributions and Quantum Oscillators
“The best thing in the world”-V, 2018/4/7
For a Quantum Oscillator, energy is discretized by 𝜖=hf and 𝑈 𝑞 =𝑞𝜖= 𝑘 𝐵 𝑇=qhf
Total number of states given N oscillators and q energy quanta Ω 𝑁,𝑞 = 𝑁−1+𝑞 ! 𝑞! 𝑁−1 !
𝑆=𝑘 ln Ω Δ𝑆(𝑞→𝑞+1)=𝑘 ln 𝑞+𝑁 𝑞+1 ≈𝑘 𝑁 𝑞 𝑇 = d𝑆 d𝑈 ≈ 𝑘𝑁 𝑞ℎ𝑓
Probability of State having energy 𝐸 𝑛 : 𝑃 𝐸 𝑛 = 𝑒 − 𝐸 𝑛 𝑘 𝐵 𝑇 𝑍
Partition function: 𝑍= Σ 𝑎𝑙𝑙 𝑠𝑡𝑎𝑡𝑒𝑠 𝑒 − 𝐸 𝑛 𝑘 𝐵 𝑇
REMEMBER TO TAKE INTO ACCOUNT DEGENERACY!!!
“Actually the Partition function is my favorite thing in the world”-V, 10 mins later R S

10. More 213 Stuff
Atmospheres: Δ𝑈=𝑚𝑔ℎ therefore 𝑃 ℎ 𝑃 0 = 𝑒 − 𝑚𝑔ℎ 𝑘 𝐵 𝑇 and <ℎ> = 𝑘 𝐵 𝑇 𝑚𝑔
“You get this from the Boltzmann distribution, the best thing in the world”-V, 30mins later

11. Exam Advice
When doing problems, PLEASE PLEASE PLEASE CHECK YOUR UNITS!!!
You will be shocked how many questions you can solve just matching units and having an idea of what they are asking for
Know when and how to use your equation sheet
Don’t panic, just keep on moving
Make sure you are in the right mindset going into the exam
Spend your time showing what you know
DON’T CHEAT

12. Spring 2015

13. Spring 2018

14. Spring 2015

15. Spring 2018

16. Spring 2015

17. Fall 2014

18. Spring 2018

19. Fall 2014

20. Fall 2014