1. Thermodynamics
Section 1

2. Overview
This chapter relates internal energy (energy of particle motion and particle distances), heat, and work

3. Thermodynamics
The study of heat and its transformation into mechanical energy

4. Absolute zero
No more energy can be extracted from a substance and its temperature cannot be lowered anymore

5. Heat, Work, and Internal energy
Heat and work are always energy transferred to and from a system
Substance can only contain internal energy
I.E. is used to do work

6. Heat, Work, and internal energy
System- a substance or combination of substances
Ex: Balloon, flask, and burner
Environment- conditions and influences that affect the behavior of a system

7. Work done by a gas
Work done on or by a gas is pressure multiplied by volume change
W = PΔV
Work = pressure x volume change
*SI unit: Joules

8. Work done by a gas cont’d
If a gas expands, ΔV and the work done by the gas are positive
Expansion = “+” work and volume change

9. Work done by a gas
If a gas is compressed, ΔV and the work done by the gas are negative
Compression = “-” work and volume change

10. Work done by a gas
If the gas volume stays constant there is no displacement and no work done

11. Example
An engine cylinder has a cross-sectional area of m². How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 7.5 x 10⁵ (750,000) Pa on the piston and moves the piston a distance of m?

12. Isovolumetric process
Constant-volume process
Occurs when a gas experiences a change in temperature but not in volume, no work is done
Example:
Water heated in a concrete container

13. Isothermal Process Constant temperature process
Occurs when the temperature remains constant and the internal energy does not change when heat or work is transferred
Example: Expansion of a balloon when barometric pressure drops (before a storm)

14. ADIABATIC PROCESS
Process where changes occur but no energy is transferred to or from the system as heat
This can be done by performing the process rapidly so the heat has little time to enter or leave (bicycle pump) or thermally insulate it
Ex: Thermally insulated balloon and tank containing compressed gas or wrapping something in Styrofoam

15. When a gas is adiabatically compressed it gets warmer b/c it gains heat
When a gas adiabatically expands it loses heat and gets cooler
You try it! Place your hand in front of your both and blow out warm air with your mouth wide-open. Repeat this but only open your mouth a little.
What do you notice?

16. Chapter 10 Thermodynamics
Section 2

17. First Law of thermodynamics
Principle of energy conservation that takes into account a system’s internal energy as well as work and heat
Sum it up:
Whenever heat is added to a system it transforms to an equal amount of another type of energy.

18. You put an airtight can full of air on a hot stove and heat it up
You put an airtight can full of air on a hot stove and heat it up. The can has a fixed volume and will not move, so no work is done.
The internal energy of the can is so the temp.
However, if you attached a piston to the can so it could do work the internal energy of the can would be less b/c some of the energy is transformed into work.

19. Equation ΔU = Q – W Change in internal energy = heat – work
All units in Joules

20. Example
A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed from the refrigerant as heat?

21. Cyclic Processes
Thermodynamic process where a system returns to the same conditions it started in
Ex: Refrigerators and Heat Engines

22. Heat Engine Changes internal energy  mechanical work
Basic Idea: Heat flows from high temp.  low temp.

23. Chapter 10 Thermodynamics
Section 3

24. If we place a hot brick next to a cold brick what do we expect to happen? What if the hot brick absorbed all of the heat from the cold brick and became even hotter… does this violate the first law of thermodynamics?

25. No it will not. The total amount of energy will remain the same
No it will not. The total amount of energy will remain the same. It will however violate the second law of thermodynamics.

26. Second Law of Thermodynamics
Basically:
Heat will never, of itself, flow from a cold object to a hot object.
Meaning…
If you want heat to flow from cold to hot you have to impose external effort (you have to do some work on it!)

27. Examples Heat pumps that increase the air temperature.
Air conditioners that reduce air temperature.

28. It’s easy to change work completely into heat, try it… Rub your hands together quickly and they will warm up. It is impossible to completely convert heat into work… The best you can do is convert SOME heat into mechanical work.

29. Heat Engine That is where the heat engine comes into play
Changes internal energy into mechanical work

30. Heat engine process
Absorbs heat from a reservoir of higher temperature (increases the internal energy)
Convert some of this energy into mechanical work
Expel the remaining energy as heat to some lower-temperature reservoir

31. When discussing heat engines, the 2nd Law of Thermodynamics may be stated:
When work is done by a heat engine running between two temperatures, Thot and T cold, only some of the input heat at Thot can be converted to work, and the rest is expelled as heat at Tcold

32. The expelled heat could be in the form of hot steam
When expelled heat is undesirable (hot steam on a hot day) it is called thermal pollution.

33. Before the development of the 2nd Law of Thermodynamics it was thought that a LOW FRICTION heat engine could convert nearly all input energy into mechanical work.
Sadi Carnot, French engineer, said he didn’t think so in 1824.

34. Carnot efficiency AKA the ideal efficiency equation.
Ideal eff. = Thot - Tcold
Thot
He said that under ideal conditions only 25% of the internal energy is converted into work and the other 75% is expelled as waste.

35. Order tends to disorder
Organized energy degenerates into disorganized energy
Ex: Gasoline  exhaust fumes

36. Application of 2nd Law
Could be restated to apply here as the following:
Natural systems tend to proceed toward a state of greater disorder

37. Entropy Measure of the amount of disorder in a system
Disorder increases, Entropy increases

38. Entropy
The second law says that when things are left to themselves, over time, they will run down and become disorganized.

39. The laws of Thermodynamics have been sometimes put this way:
You can’t win (because you can’t get any more energy out of a system than you put in), you can’t break even (because you can’t even get as much energy out as you put in), and you can’t get out of the game (entropy in the universe is always increasing).