Ch15:
Thermodynamics
Or, “Let’s try to remember all that
stuff we learned last year, K!”
Seriously…
• Whatsup?
–Ch 13, 14, & 15 simultaneously
–Regular HW each chapter.
• DUE DATES? Check CALENDAR!
Heat & Thermodynamics
Ch 15 – Thermodynamics
Basic LAWS
• 0th Law
–Two systems individually in thermal
equilibrium with a 3rd system are in
equilibrium with each other.
–Sorta like
• If A=B & B=C, then A=C
Online Thermal Thing
Figure 15.3, 1st Law of T
•
The first law of thermodynamics is the conservation-of-energy principle stated for a system where heat and
work are the methods of transferring energy for a system in thermal equilibrium. 𝑄 represents the net heat
transfer—it is the sum of all heat transfers into and out of the system. 𝑄 is positive for net heat transfer into the
system. 𝑊 is the total work done on and by the system. 𝑊 is positive when more work is done by the system
than on it. The change in the internal energy of the system, Δ𝑈 , is related to heat and work by the first law of
thermodynamics, Δ𝑈 = 𝑄 − 𝑊 .
Figure 15.3
•
The first law of thermodynamics is the conservation-of-energy principle stated for a system where heat and
work are the methods of transferring energy for a system in thermal equilibrium. 𝑄 represents the net heat
transfer—it is the sum of all heat transfers into and out of the system. 𝑄 is positive for net heat transfer into the
system. 𝑊 is the total work done on and by the system. 𝑊 is positive when more work is done by the system
than on it. The change in the internal energy of the system, Δ𝑈 , is related to heat and work by the first law of
thermodynamics, Δ𝑈 = 𝑄 − 𝑊 .
• 1st Law
Basic LAWS
–Internal energy of a system changes
from an initial value Ui to a final value
Uf due to heat Q and work W:
•  U = Uf – Ui = Q + W
• Q>0 when system gains heat & <0 when
it loses heat.
• W>0 when work is done ON system & <0
when gas does work.
•
Basic LAWS
st
1
Law
–Internal energy of a system changes
from an initial value Ui to a final value
Uf due to heat Q and work W:
• Q = Heat transferred to a system.
• W = Work done ON a system
QIN > 0
QOUT < 0
WON > 0
WBY < 0
QIN > 0
QOUT < 0
WON > 0
WBY < 0
Using the 1st LAW
• 2500J of heat is added to a system, and 1800J
of work is done on the system. Find change in
internal energy of the system?
U  Q  W
U  2500 J  1800
U  4300 J
Basic LAWS
• 1st Law Example (p427)
–T of 3 mol is reduced from 540K to
350K by adding 5500J of heat to it.
• Find U & W done by or on gas.
–T of 3 mol is reduced from 540K to
350K by adding 5500J of heat to it.
• Find U & W done by or on gas.

3
U  nRT
2

3
 (3mol ) 8.31 J
(350  540 K )
mol  K
2
 7100 J
–T of 3 mol is reduced from 540K to
350K by adding 5500J of heat to it.
• Find U & W done by or on gas.
U  W  Q
W  U  Q
 7100 J  5500 J
by or on gas?
 12,600 J
Using the 1st LAW
• Work done on or by a gas?
WBY  Fd  PAd
WBY  PV
PV Diagrams
1st Law Thermal Processes
• Isobaric
– Constant P
• W=PV
• Isochoric (Isovolumetric)
– Constant V
• Isothermal
– Constant T
• Adiabatic
– No transfer of heat
Thermal Processes
• Isobaric
Copied from Emile Clapeyron’s Bio (1799 - 1864).
Thermal Processes
• Isochoric
Copied from Emile Clapeyron’s Bio (1799 - 1864).
Thermal Processes
• Isothermal
Copied from Emile Clapeyron’s Bio (1799 - 1864).
Thermal Processes
• Adiabatic
Copied from Emile Clapeyron’s Bio (1799 - 1864).
Thermal Processes
• Since W=PV, Work is area under P/V
graph.
1st Law Thermal Processes
• Isobaric
– Constant P
• W=PV
• Isochoric
– Constant V
• Isothermal
– Constant T
• Adiabatic
– No transfer of heat
Using the 1st LAW
• Efficiency of a heat engine?
W
Q
e
 1
Q
Q
L
H
H
Using the 1st LAW
• Ideal efficiency (Carnot Engine)?
T
e  1
T
L
ideal
H
Carnot (IDEAL) Engine
Carnot (IDEAL) Engine
eCarnot
TH  TL
TL

 1
TH
TH
Basic LAWS
• 2nd Law
–Heat flows from a substance at
higher temp to a substance at
lower temp and does NOT flow in
the reverse direction. Ever.
Basic LAWS
• 2nd Law & Entropy
• Entropy, disorder or randomness, of
the Universe increases
Q
S 
T
S  0
Basic LAWS – 2nd
• The total entropy of a system PLUS
the environment increases as a
result of heat flow.
Q
S 
T
S  0
Basic LAWS
• 3rd Law
–Absolute Zero is impossible to
reach in a finite number of steps.
Ch 13-15
• HW Posted.
• PSS next 1-2 classes