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Q1.
A system’s internal energy falls by 200J as a result of energy transfer and work being done. The system
does 500J of work on the surroundings.
a) State and explain whether the system is at a higher or lower temperature than its surroundings.
b) Calculate the amount of energy transferred causing the reduction in internal energy.
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Q2.
a) Distinguish between an isothermal process and an adiabatic process as applied to an ideal gas.
b) An ideal gas is held in a cylinder by a moveable piston and energy is supplied to the gas such that
the gas expands at a constant pressure of 1.5 × 10^5 Pa. The initial volume of the cylinder is 0.040
m^3 and its final volume is 0.12 m^3. The total energy supplied to the gas during the process is 7.5 ×
10^3 J.
(i) State and explain the type of change that the gas undergoes.
(ii) Determine the work done by the gas.
(iii) Calculate the change in internal energy of the gas.
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Q3.
An ideal gas expands adiabatically from a state with pressure 5.00 × 10^5 Pa, volume 2.20 × 10^−3
m^3 and temperature 485 K to a new volume of 3.80×10^-3 m^3 . Calculate the new pressure and
new temperature of the gas.
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Q4.
A gas is compressed at a constant pressure of 2.00 × 10^5 Pa from a volume of 2.00 m^3 to a volume
of 0.500 m^3 . The temperature is initially 40.0°C.
a. Find the work done.
b. Calculate the final temperature of the gas.
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Q5.
An ideal gas expands adiabatically,
a Explain why the temperature decreases.
b Use your answer to a to explain why the adiabatic curve of an ideal gas, expanding from a given
state, is steeper than the corresponding isothermal curve from the same state.
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Q6.
An ideal gas, kept at a constant pressure of 3.00×10^6 Pa, has an initial volume of 0.100m^3 . The gas
is compressed at constant pressure down to a volume of 0.080m^3 .
Find
a) the work done on the gas and
b) the energy transferred.
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Review
Mark Zemansky:
"Teaching thermal physics
is as easy as a song:
You think you make it simpler
when you make it slightly wrong."
Mark Zemansky:
"Teaching thermal physics
is as easy as a song:
You think you make it simpler
when you make it slightly wrong."
Little idea about what we are going to learn here today....
Second Law of Thermodynamics
Entropy and Energy Degradation
Heat Engines & Heat Pumps
Carnot Cycles
Carnot Theorem
We already talked about 1st Law of Thermodynamics which is
nothing but the Law of Conservation of Energy now Lets try to
start with 2nd Law of thermodynamics...What is it???
How does it relate to entropy???
What is Entropy???
Why at all we should talk about entropy in thermal physics ??
Have we heard about Heat engines...Heat Pumps n all...what are
they ??? How do they function ???
Questions more Questions...
Okkk ? Let me raise sm situations...
When a body at 100 c is kept in contact with a similar body at 0 C, heat flows
from the hotter body to the colder body and both come to 50 Is the reverse
process possible ? That is, if we put two similar bodies both at 50 , in contact
can heat flow from one body to the other so that one reaches 0 and the other
100 ?? All by itself (spontaneously)???
A block moving at a speed v on a rough table eventually stops, the table and the block warms
up. The kinetic energy of the block appears as the internal energy of the table and the block. Can
the reverse process be possible ??? That is if we heat the block and the table and put the block
on the table. Can the bodies cool down and the block starts sliding with speed v on the table
converting the internal energy into K.E.???
The answer to all these questions is a big
NO
The first law of thermodynamics (conservation of energy) would not be violated if any of these processes
occurred in reverse. To explain this lack of reversibility, scientists in the latter half of the nineteenth century
formulated a new principle known as the second law of thermodynamics.
See
this picture
pistooder
Moreader
This is an important picture which is actually showing the connection between the entropy and the 2nd
Law of thermodynamics...
So we are trying to connect two scenarios here...one is that despite the conservation of energy being
valid we still cannot have certain processes happening spontaneously...
so we definitely have to frame some different law which can take care of such situations where although
law of conservation holds but things are still not right..
second thing is quite evident from the picture where we see that process is actually not possible if it has
to go from disorderness to orderness ...
What is we see above was that process can actually proceed from order to disorder and thats
interesting but NOT reversing spontaneously...
Infact now we will be relating the term Entropy to disorderness & will try to frame 2nd Law as
well...
Although the words clearly speak for the meaning of order and disorder but we must have more
insight as to what order and disorder actually mean in thermodynamics...
We must talk about something called as the multiplicity..
000000000
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Better take an example...
Time
Ffropy
high
Entropy
Entropy & Time !!!
Lot of research has been done in the past to relate entropy to the time arrow....
E
Many more interesting articles can be found online on entropy & time...infact entropy is
extremely important for deeper understanding of artificial intelligence...and much more!!!
Why 2nd Law of Thermodynamics is so important...???
Let’s start by quoting one of the pioneer in the field Prof. Arthur Eddington...
Various forms in which 2nd Law usually occurs in textbooks...
Clausius
Planck
Kelvin
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out
Let’s talk more on Heat Engines/Pumps, the reversible and irreversible cycles,
Carnot cycle and Relation between Entropy, Heat and Temperature...
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In 1824 the French engineer Sadi Carnot investigated how to convert heat into useful mechanical
work in the most efficient way. We know that we cannot have a 100% efficient engine, but is there
a limit to how efficient an engine can be? Carnot showed that there is....
The Carnot cycle consist of two isothermals and two adiabatics.
The engine starts its cycle in state 1.
The gas is compressed isothermally to state 2.
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During this stage, heat QC leaves the gas and
THO
work is done on the gas. From state 2 to state 3
the gas is compressed adiabatically; work is again
done on it. From state 3 to state 4 the gas
expands isothermally, receiving heat QH from a
2 From state
hot reservoir; work is done by the gas.
T
AQ co
4 to state 1 the gas expands adiabatically; work is
done by the gas. The net work done by the
engine is therefore:
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The temperature along the isothermal 3→4 is TH, and along the
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isothermal 1→2 it is TC. The total change in entropy of the engine is:
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Carnot’s engine has an efficiency less than 1 (that is, 100%). It would be 100% only in the
impossible cases of TC = 0 or TH = ∞.
7
It can be shown that the following statement is yet another formulation of the second law of
thermodynamics:
No engine is more efficient than a Carnot engine operating between the same temperatures.
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