The document discusses the laws of thermodynamics: 1) The 0th law states that if two systems are in thermal equilibrium with each other, they must be in equilibrium with a third. 2) The 1st law relates the internal energy of a system to heat and work. It states that the change in internal energy is equal to the heat added plus work done. 3) The 2nd law states that the entropy of an isolated system always increases, and heat naturally flows from hotter to colder bodies.

1. Thermodynamics
Chapter 10

2. 0th Law of Thermodynamics
If system A is in thermal equilibrium with system B, and
system B is in thermal equilibrium with system C, then
system A must be in thermal equilibrium with system C.

3. 1 Law of Thermodynamics
st
Conservation of Energy for Heat!
Involves three energies:
Work, Heat, Internal Energy
Internal energy = heat added to the
system + the work done on the system.
∆U = Q + W Sign Conventions:
Heat added + Work on system +
Heat lost – Work by system –

4. U, Q, and W
U = Internal energy
 depends on change in temperature
Q = Heat
 depends on transfer of heat energy
W = Work
 W = F•d = P A d = P ∆V
(P = F/A)

5. 4 Different Events
Isobaric
 Constant Pressure
Work is done by
expanding volume
Example:
∆U = Q + W Brick on top of sealed
∆U = Q + P∆V canister.
Same force over same area
∴ pressure doesn’t change.

6. Isochoric (isometric)
 Constant volume
All heat changes into
internal energy
If ∆V = 0, then W = 0
∆U = Q + W
∆U = Q + 0 Examples:
Inside Pressure Cooker,
∆U = Q Mist above soda.
Volume stays the same. Pressure
rapidly decreases.
Temperature rapidly decreases
causing the gas to be pushed out

7. Isothermal
 Constant Temperature
Heat is converted to
mechanical work
If ∆T = 0, then ∆U = 0
∆U = Q + W Example:
0=Q+W Boiling Water
Q = –W

8. Adiabatic (Greek
Adiabatos: Impassable)
 No heat transfer
System is extremely well
insulated or process
happens so fast that heat
doesn’t have time to flow
in or out
If no heat transfer, Q = 0 Example:
Stretching rubber band
∆U = Q + W quickly – Not enough time
∆U = 0 + W for heat transfer, so the
∆U = W work done goes into
internal energy.

9. Sample 2
The internal energy of the gas in a gasoline
engine’s cylinder decreases by 195 J. If 52.0 J of
work is done by the gas, how much energy is
transferred as heat? Is this energy added to or
removed from the gas?
∆U = Q + W
-195 = Q + -52.0
Q = -143 J  because it is negative it is removed

10. 2nd Law of Thermodynamics
High Temp
Engine
Work
Low Temp
Heat Engines  any
device that changes
heat energy to
mechanical energy

11. Entropy (S)
 measure of the disorder of a system
Entropy of a system tends to increase. (Become more
disordered)
Another statement of the 2nd Law
 Natural processes tend to move toward a state of
greater entropy.
R.J. Clausius (German physicist, 1822-1888)
Said 2nd Law deals with the direction a process will go
Clausius’ Statement of 2nd Law of Thermo.
 Heat flows from hot  cold

12. Most general form:
Natural processes tend to have a preferred
direction in which they tend to move.
ie. An apple doesn’t jump up to a tree, hot
water does not get cold over a fire, etc.
3rd Law of Thermodynamics
It is impossible to reach Absolute Zero.