1 / 20

Review from Last Lecture

Review from Last Lecture. State Equation of Ideal Gas Kinetic Theory Boltzmann’s Constant Avagadro’s Constant Ideal Gas Constant Distributions Mean Boltzmann Distribution Maxwell-Boltzmann Velocity Distribution. Velocity Distribution. Different velocities. Review from Last Lecture.

ainsworth
Download Presentation

Review from Last Lecture

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Review from Last Lecture • State Equation of Ideal Gas • Kinetic Theory • Boltzmann’s Constant • Avagadro’s Constant • Ideal Gas Constant • Distributions • Mean • Boltzmann Distribution • Maxwell-Boltzmann Velocity Distribution

  2. Velocity Distribution • Different velocities

  3. Review from Last Lecture • Thermodynamics • The study of changes to the state of a system • State variables: Pressure, Volume, Temperature • Heat (Q) and work (W) are both measures of energy flowing into and out of the system • 1st Law of Thermodynamics • Types of State Changes • Isochoric (volume constant) • Isobaric (pressure constant) • Isothermal (temperature constant) • Adiabatic (no heat flow)

  4. Isochoric Processes • In an isochoric process, no work is done because the volume doesn’t change

  5. Specific Heat (Constant Volume) • Define a specific heat as heat required to raise temperature of one mole by one degree (K):

  6. Isobaric Processes • In an isobaric process, the work is easy to calculate because the pressure doesn’t change

  7. Specific Heat (Constant Pressure) • We define a new specific heat for changes at constant pressure • Some of the heat flowing into the system is used to do work so

  8. Isothermal Processes • If the temperature is constant, the internal energy is also constant

  9. Adiabatic Processes • In an adiabatic process, there is no heat flow • Use the state equation

  10. Adiabatic Processes

  11. Adiabatic Processes • Another derivation

  12. The 2nd Law of Thermodynamics This conserves energy! Tc Th  Q • Why do we need a second law? • The 1st Law allows heat to flow from cold to hot (it doesn’t actually distinguish between work and heat)

  13. The 2nd Law of Thermodynamics • Two ways of stating 2nd Law • Kelvin-Planck: It is impossible to construct an engine that converts a given amount of heat into an equivalent amount of work • Clausius It is impossible to transfer heat from a lower temperature to a higher temperature without doing work • Actually these are identical

  14. Another State Variable? • State variables depend one on the “state” of the gas • This really means that in moving from one state to another the change in a state variable depends only on the beginning and ending states • Temperature (energy) is a state variable but work and heat (changes in energy) are not Can integrate this Can’t integrate these (because T is independent of V)

  15. Another State Variable? • But we can transform the heat into a state variable • Just divide out the temperature • This is the entropy (S) of a given state and it is a state variable Can’t integrate this Can integrate this

  16. The 2nd Law of Thermodynamics • Another way of stating the 2nd Law • Entropy: It is impossible to reduce the entropy of an isolated system The entropy of the universe always increases

  17. Allowed Processes Q  Tc Tc Th Th • Only processes allowed by the 2nd Law are observed to happen • Example: Heat Flow • Allowed (Heat Transfer, Hot to Cold) • Disallowed (Perfect Refrigerator) Q 

  18. Allowed Processes • Example: Free Expansion/Contraction • Allowed • Disallowed  

  19. The 2nd Law as a Statistical Law • Unlike other laws of physics, the 2nd law of Thermodynamics is only true in a statistical sense • What’s the probability all the molecules are on the left? • For 1 molecule: 1/2 • For 2: 1/4 • For 3: 1/8 • For NA:

  20. The 2nd Law as a Statistical Law • Unlike other laws of physics, the 2nd law of Thermodynamics is only true in a statistical sense • But the probabilities are truly astronomical • The 2nd Law is also asymmetric with respect to time • Make a movie of an elastic collision; can run movie backward, it looks realistic • Newton’s Laws has “Time Reversal Symmetry” • Make a movie of dye dispersing in a liquid (which is governed by the 2nd Law); can’t run it backward • 2nd Law gives “arrow of time”

More Related