5. Benjamin Thompson a.k.a Count Rumford
Cannon Boring Experiment
“There is a relationship
between heat and work”
“I can’t quantify my
findings” ☹
6. James Prescott Joule
“Heat is just another form
of energy and that it is
related to work”
Work W
Heat Q
J = =
7. First Law of Thermodynamics
“The total heat energy applied to a closed
system is equal to the sum of the change in
internal energy and work done”
Q = U + W
8. Sample Problem
1. 3000 J of heat is added to a system, and 2500 J
of work is done by the system. What is the
change in internal energy of the system?
Note:
• Q is positive if the heat is added to the system
• Q is negative if heat leaves the system
• W is positive if work is done by the system
• W is negative if work is done on the system
9. Sample Problem
1. 3000 J of heat is added to a system, and 2500 J
of work is done by the system. What is the
change in internal energy of the system?
Given:
• Heat (Q) = + 3000 Joule
• Work (W) = + 2500 Joule
• Unknown = Internal Energy of the System
Equation: U= Q-W
Solution:
• U = 3000 – 2500
U= 500 Joule
12. Conditions of a closed system:
b. Isothermal expansion- temperature is
constant.
c. Isobaric system- pressure is constant.
d. Isochoric system- volume is constant.
a. Adiabatic process- no heat is added or
removed from the system.
13. Sample Problem
2. A certain system does 350 J of work. How much heat
is absorbed if the change in the internal energy of the
system is 50 J?
14. Sample Problem
1. Calculate the change in internal energy on the
system when 140J of heat are observed and 85 J of
work are done.
15. Heat Engines
-convert heat into mechanical energy
External-combustion
Engine
Internal-combustion
Engine
Steam Engine Gasoline Engine
Diesel Engine
16. Steam Engine- is a heat engine that
performs mechanical work using steam as its
working fluid.
17. Gasoline Engine- uses a spark ignition system
to generate an electrical charge with spark plugs
that ignites the fuel and air inside a cylinder
resulting in fuel combustion
18. Diesel Engine- is an engine in which ignition of
the fuel that has been injected into the combustion
chamber is caused by the high temperature which a gas
achieves when greatly compressed
19.
20. Second Law of Thermodynamics
“Heat flows spontaneously from higher to
lower temperature”
“Only some of the heat can be converted
into work”
ENTROPY
26. Heat Engine and Mechanical Work
High
Temperature
Heat
Input
Heat
Engine
Work done
Low
Temperature
27. Nicolas Leonard Sadi Carnot
“The greatest fraction of energy
input that can be transformed
into useful work depend on the
temperature difference between
hot and cold reservoirs”
W
QH
28. Sample Problem
2. A heat engine takes in 900 J of heat from a
high temperature reservoir and produces 300 J
of work in each cycle. What is its efficiency?
Given,
• Qh=900J
• W=300J
Unknown: Efficiency
Equation:
• Solution:
- 300 J / 900 J x 100 %
• 0.33 x 100
• 33 %
29. Sample Problem
3. An engine that has an efficiency of 25% takes in
200 J of heat during each cycle. Calculate the amount
of work this engine performs.
30. Sample Problem
1. What is the maximum possible
efficiency of a heat engine that
operates between 27°C and 127°C?
31. Sample Problem
4. A heat engine takes in 700 J of heat from
a high temperature reservoir and rejects 500
J of heat to a lower temperature reservoir.
How much work does the engine do in each
cycle? Calculate the efficiency of the engine.
32. ENTROPY AND THE SECOND LAW OF
THERMODYNAMICS
>During energy transformation:
Organized
Energy
Transformation of
energy
Disorganized
Energy
ENTROPY
33. HEAT PUMP
-a device that transfers heat from a colder area to a hotter
area by using mechanical energy.
36. Third Law of Thermodynamics
“ The entropy of a pure crystalline substance is
zero at 0 K (absolute zero)”
T= 0 K
S= 0 S>0
T>0 K
37.
38. Zeroth Law of Thermodynamics
“ If the two systems are each in thermal
equilibrium with the third system, they are also
in thermal equilibrium with each other”
A B
=
then
B = C
and
A C
=
What’s your
conclusion?
