9093654.ppt thermal grade 10 physics notes

thermodynamis

1. First Law of
Thermodynamics
Please hand in your Labs at the front of room
Take out a piece of paper
No need for notes!

2. Thermodynamic Process
A thermodynamic process is one in which heat is added to or taken
away from a system. ΔQ = change in heat
 Any system has some internal energy (ΔU) state. The energy state is
defined by the systems temperature (T), volume (V), and pressure (P)

3. Laws of Thermodynamics…. kind of….

4. Zeroth Law of Thermodynamics
Zeroth: Two systems are at thermal equilibrium if they have the
same temperature.
The significant consequence of the Zeroth Law is that, when a
hotter object and a colder object are placed in contact with one
another, heat will flow from the hotter object to the colder object
until they are in thermal equilibrium.

5. First Law of Thermodynamics
First: also known as Law of Conservation of Energy, states that energy can not
be created or destroyed; it can only be redistributed or changed from one form to
another.
ΔU = Q + W
ΔU is the change in internal energy of the system, Q is the heat added to
the system, and W is the work added to the system
Q is positive when it is added to the system and negative if it is taken out
of the system.
Output Work (done on other systems) is negative
Input Work (done on the system) is positive

6. Sign Convention
ΔU = Q + W
 +Q when heat is added to the system.
 - Q when heat is lost from the system.
 +W when work is done on the system.
 - W when work is done by the system.

7. Second Law of Thermodynamics
Second: The entropy of a closed system never decreases as time
goes by. Reversible processes do not change the entropy of a
system, while irreversible processes increase a system’s entropy.
S ≥ 0
S = Entropy of a System

8. When we discuss these Laws think of….
Zeroth: Temperature Exists and therefore you must
play the game.
Heat will flow from hot to cold always and forever.
First: You can't win.
You can't get more energy out of a heat engine than you put in.
Second: You can't break even.
No heat engine can use all the heat produced by a fuel to do work.

9. First Law Question
In a thermodynamic process, a system absorbs 450 kJ of heat and does
87 kJ of work on its surroundings. By what amount did the system’s
internal energy change?
ΔU = Q + W

10. First Law Question
In a thermodynamic process, a system absorbs 450 kJ of heat and does
87 kJ of work on its surroundings. By what amount did the system’s
internal energy change?
ΔU = Q + W
Note that the work done by the system ON the surroundings is
negative.

11. First Law in a “Nutshell”
Here is a diagram of a generic
thermodynamic process.
A system has an initial internal energy.
Heat (Q): can be added to the system, or
taken away from the system or there may
be no heat transfer.
Work (W): may be done on the system or
the system may do work or there may be no
work involved at all.
Internal Energy
U1
T1P1 V1
Internal Energy
U2
T2P2 V2
Thermodynamic
Process
Q
W

12. For everything we are about to do….
Always keep in mind the Ideal Gas Law…
PV = nRT

13. Isobaric Process
Greek for…
“Iso” – refers to something remaining constant
“Baric” refers to pressure
Collect and read the handout from the front and read the

14. The 4 “`Processes” ~ cases of the First Law
Isothermal Process – thermodynamic process in which the temperature of the
system remains constant.
•Occurs often in heat reservoirs (surrounds can supply or soak up excess heat)
Adiabatic Process – thermodynamic process in which no heat is exchanged
between the system and its environment.
•Occurs rapidly or when well insulated (think a thermos!)
Isobaric Process – thermodynamic process in which the pressure of the
system remains constant.
Isochoric Process – thermodynamic process in which the volume of the
system remains constant.

15. Please collect a Whiteboard and Pens and draw
the following!
PV = nRT PV = nRT

16. For the following P vs. V diagram… determine
which of the Special Cases applies
A.Isobaric: pressure is constant
Is the 1
st
Law Equation affected by an
Isobaric process?
No!
W = PΔV
Work can be done if the volume of the
system undergoes a change.
P
V
A.

17. Video

18. For the following P vs. V diagram… determine
which of the Special Cases applies
B.Isochoric: Volume is constant (taking
up the same space)
How does the 1
st
Law Equation change
during an Isochoric process?
In this type of process, the volume stays
constant. This means that ΔV is zero. If
ΔV is zero, then the work must also be
zero.
P
V
B.

19. For the following P vs. V diagram is an Adiabatic Process
C.Adiabatic Process: no heat is exchanged
between the system an its environment
How does the 1
st
Law Equation change
during an Adiabatic process?
ΔQ = 0
P
V
C.

20. For the following P vs. V diagram is an Isothermal Process
D.Isothermal Process: Temperature is
constant
How does the 1
st
Law Equation change
during an Isothermal process?
The isothermal process happens at a
constant temperature. The pressure and
volume change, so work is done, but ΔU is
zero.
D.
P
V
PV = nRT = constant!

21. Summary of Processes

22. What now?
1.Collect Worksheet for 1
st
Law of Thermodynamics – Key Posted
2.Watch the notes for the four species cases of the 1
st
Law!
3.Next Class: Heat Engines