1. Changes of Phase
List the four phases of matter in order of increasing internal energy

2. Changes of Phase
List the four phases of matter in order of increasing internal energy
solid => liquid => gas => plasma
List the processes that take you from a solid to a plasma

3. Changes of Phase
List the four phases of matter in order of increasing internal energy
solid => liquid => gas => plasma
List the processes that take you from a solid to a plasma
melting => evaporation => ionization
List the processes that take you from a plasma to a solid

4. Changes of Phase
List the four phases of matter in order of increasing internal energy
solid => liquid => gas => plasma
List the processes that take you from a solid to a plasma
melting => evaporation => ionization
List the processes that take you from a plasma to a solid
electron capture => condensation => freezing

5. Evaporation and Boiling
A phase change from liquid to gas at the surface of a liquid
Which molecules are most likely to escape surface?
Boiling
Evaporation beneath the surface of a liquid
Vapor pressure must balance surrounding pressure – boiling point
How does boiling point change with altitude?

6. Condensation A phase change from a gas to a liquid
Opposite of evaporation
Since evaporation (and boiling) are cooling processes, is condensation a warming process?

7. Condensation A phase change from a gas to a liquid
Opposite of evaporation
Since evaporation (and boiling) are cooling processes, is condensation a warming process?
Yes. Gas molecules near surface of a liquid are attracted to the liquid => collide with greater K.E. => temperature of liquid rises
Water condenses on the outside
of a cold soda can and warms the
soda in the process.

8. Melting and Freezing Melting Freezing (reverse process)
Random thermal motion at high temp. breaks molecular bonds
Freezing (reverse process)
Decreased motion allows binding due to interparticle attraction
Regelation
Continued melting and refreezing of water under pressure
Ex. Ice skating
What special property of water makes this possible?
Regelation – the wire will slowly
pass through the ice without cutting
it in half.

9. Melting and Freezing Melting Freezing (reverse process)
Random thermal motion at high temp. breaks molecular bonds
Freezing (reverse process)
Decreased motion allows binding due to interparticle attraction
Regelation
Continued melting and refreezing of water under pressure
Ex. Ice skating
What special property of water makes this possible?
Density of ice less than that of water => melts under pressure!
Regelation – the wire will slowly
pass through the ice without cutting
it in half.

10. Temperature and Phase Changes
Temperature is constant during a change of phase
Absorbed heat goes into breaking molecular bonds => increased potential energy. Translational K.E. remains unchanged. (Left to Right)
Extracted heat allows molecular bonds to form (decreased potential energy) at fixed temp. (Right to Left)
A material absorbs energy when melting
or vaporizing and expels energy when
condensing or freezing.
During a phase change, the energy
goes into the change of state rather than
into changing the object's temperature.

11. Thermodynamics
The study of heat and its transformation to mechanical energy and work
1st law of thermodynamics
When heat flows into (or out of) a system, the system gains (or loses) an amount of energy equal to the amount of heat transferred.
ΔHeat = ΔInternal Energy + Work
Adding heat to a system can:
increase the internal energy of the system
enable the system to do external work (or both)
Device demonstrating the
conversion of mechanical
energy to heat energy

12. 1st Law (cont.)
What fundamental principle in physics does the 1st law express?

13. 1st Law (cont.)
What fundamental principle in physics does the 1st law express?
Conservation of energy (ΔHeat = ΔInternal Energy + Work)
Holds for all systems, regardless of the specifics of their inner workings
Adding heat
to fixed volume (sealed container of air)
How does the temperature and pressure of the air change?
How much work is done? Where does the energy go?
to changeable volume (e.g. Piston)
What happens to the piston?

14. 1st Law (cont.)
If we do mechanical work on a system, we can also increase its internal energy
Your hands get warmer if you rub them together
What happens to the air in a bicycle pump as the handle is pushed down?

15. 1st Law (cont.)
If we do mechanical work on a system, we can also increase its internal energy
Your hands get warmer if you rub them together
What happens to the air in a bicycle pump as the handle is pushed down?
Air is compressed and temperature (measure of internal energy) rises
You can always transform mechanical energy completely into heat, but you can never transform heat completely into mechanical energy!
Directionality to nature of heat flow and energy

16. Imagine two bricks at different temperatures in thermal contact
If the hot brick were able to extract heat from the cold brick, would this violate the 1st law of thermodynamics?

17. 2nd Law of Thermodynamics
Imagine two bricks at different temperatures in thermal contact
If the hot brick were able to extract heat from the cold brick, would this violate the 1st law of thermodynamics?
No. Not if the cold brick becomes even colder so that the total amount of energy is conserved.
This sort of behavior is prohibited by the 2nd law of thermodynamics:
Heat never spontaneously flows from a cold object to a hotter object.
Heat can be made to flow in the opposite direction, but only by doing work on the system or by adding energy from another source.

18. Heat Engines Heat = disordered energy – random thermal motion
Alternative statement of 2nd law:
No device is possible whose sole effect is to transform heat completely into work.
There is a maximum efficiency (η < 1) for any heat engine - 3rd law
Depends only on operating temps.
It is easy to convert work entirely into heat, e.g., friction
Reverse is not possible
Some heat must always be
“wasted” (exhausted to a
low temperature reservoir)
Thot - Tcold
η =
Thot

19. If you open a bottle of perfume, what happens to the perfume molecules?

20. Entropy and Disorder
2nd Law – Systems left to themselves evolve towards states of increasing disorder
Entropy: Measure of disorder
Organized energy (e.g. gasoline) degenerates to disorganized and less useful energy (heat)
Perfume diffuses in a room – goes from organized state (all molecules in bottle) to more disordered state (all throughout room)
Defines an “arrow” of time
Microscopic laws of physics are time-reversible
Will the perfume
molecules scattered
throughout the room
ever all spontaneously
return to the bottle?

21. Entropy and Disorder (cont.)
Disordered energy can be changed to ordered energy only with organizational effort or work input
Work put into refrigeration cycle => water freezes (more ordered state)
Gas compressed into a smaller volume requires outside work to be done on the gas
Living organisms concentrate and organize energy from food sources
In each case, the entropy of the system decreases. Do these examples violate the 2nd law of Thermo?

22. Entropy and Disorder (cont.)
Disordered energy can be changed to ordered energy only with organizational effort or work input
Work put into refrigeration cycle => water freezes (more ordered state)
Gas compressed into a smaller volume requires outside work to be done on the gas
Living organisms concentrate and organize energy from food sources
In each case the entropy of the system decreases. Do these examples violate the 2nd law of Thermo?
No. In each entropy of the environment increases, which more than compensates for the decrease in entropy. The total entropy of the universe always increases (or stays the same) in any given process.