4. Zeroth Law of Thermodynamics
If objects A, B and C are in contact with each other,
and A is in thermal equilibrium with B and B is in
thermal equilibrium with C, then A is in thermal
equilibrium with C.
6. First Law of Thermodynamics
7. First Law of Thermodynamics
The change in internal energy (ΔU) is equal to the
difference of the heat (Q) added/removed to/from the
system and the work (W) done on/by the system.
ΔU = Q – W
8. Sign Conventions for the First Law
For Heat (Q)
+ if the heat is added to the system
if the heat is removed from the system
For Work (W)
+ if work is done by the system
if work is done on the system
10. Sample Word Problems on 1st Law
Suppose 2500 J of heat is added to a system and 1800 J
of work is done on the system. What is the change in
internal energy of the system?
You have a motor that absorbs 3000 J of heat while
doing 2000 J of work. What is the change in the
motor’s internal energy?
Say that a motor does 1000 J of work on its
surroundings while releasing 3000 J of heat. By how
much does its internal energy change?
13. Second Law of Thermodynamics
Review: How does heat flow?
Would it be possible for heat to flow from an area of
lower to higher temperature?
14. Second Law of Thermodynamics
Heat can flow spontaneously from a hot object; heat
will not flow spontaneously from a cold object to a hot
15. Second Law and Heat Engines
It is a machine that turns energy into mechanical
energy or motion, especially one that gets its energy
from a source of heat, such as burning of a fuel.
Can be classified as external combustion and internal
18. Water-Tube Type
It is common with
stationary engines and
Water is allowed to pass
through tubes while the
flames and hot gaseous
products of combustion
follow a path over around
19. Fire-Tube Type
Used in steam
Flames and heat are
made to enter the tubes
which are horizontally
arranged in the boiler
and are surrounded by
32. Thermal Efficiency of an Engine
It is defined as the ratio of the net work (W) done by
the engine during one cycle to the energy absorbed at
the higher temperature (QH) during the cycle.
33. Sample Problem on Thermal
Find the efficiency of a heat engine that absorbs
2000 J of energy from a hot reservoir and exhausts
1500 J to the cold reservoir.
Your car is powered by a heat engine and does 3.0 x
107 J of work getting you up a small hill. If the heat
engine is 80 percent efficient, how much heat did
it use and how much did it exhaust?
34. Sadi Carnot
A French engineer who
established the concept of an
ideal engine known as the
He developed the Carnot’s
theorem which states that No
real engine operating between
two energy reservoirs can be
more efficient than a Carnot
engine operating between the
same two reservoirs.
35. Basic Concept of the Carnot
The ideal efficiency of an engine depends on the
difference of the hot and cold reservoirs.
You can’t have it all.
36. Sample Word Problems on Carnot
If an engine extracts heat from a 2730 K reservoir and
expels heat at 1730 K reservoir, what is its efficiency?
How about if the engine extracts heat from a 10 730 K
What if the engine reservoirs are working at the same
37. Wait a minute…
It is possible to produce work from heat – that is heat
transferred from a hot reservoir to a cold reservoir.
Would it be possible to do the reverse?
38. Second Law of Thermodynamics
It is impossible to construct a heat engine that,
operating in a cycle, produces no effect other than the
absorption of energy from a reservoir and the
performance of an equal amount of work.
40. Heat Pumps
These are heat engines running in reverse.
Heat is transferred from a cold reservoir to a hot
reservoir by performing work.
This is done through the aid of phase change.
Examples are refrigerators and air conditioning units.