Importance of thermodynamics

1. Formulated By: Rooman Haseeb
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IN F O R M A T I O N EN G I N E E R I N G TE C H N O L O G Y
SUPERIOR UNIVERSITY, LAHORE
What is thermodynamics?
• A branch of physics that studies the relationship between energy and the work
of a system.
• A branch of science that deals with heat and temperature and the
interconversion of heat and other forms of energy.
• Study of energy conversion, most typically through terms of heat and work.
Examples:
• Washing machines, refrigerators, and air-conditioners.
• Thermal power plants, and nuclear power plants, based on renewable energy
are all studied in thermodynamics.
Why is it called thermodynamics?
"Thermodynamics" comes from the Greek words "therme" which means heat and
"dynamikos" which means force, or power.
Why do we study thermodynamics in physics?
It gives the foundation for heat engines, power plants, chemical reactions, and many
more important concepts that our world relies on today.
Importance of thermodynamics:

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What is the thermodynamic system?
• It is the part of the universe in which observations are made, and the remaining
universe constitutes the surroundings.
• The major interactions that occur in Thermodynamics are between the systems
and their environments.
• The universe = The system + The surroundings
Parts:
A thermodynamic system is embedded in its environment or surroundings, through
which it can exchange heat with, and do work.
System:
A thermodynamic system exchanges heat with its surroundings through a
boundary.
Boundary:
The boundary is the wall that separates the system and the environment.
Surrounding:
Everything that interacts with the system.
Thermodynamic systems can exchange energy or matter with the external
environment and can also undergo internal transformations.

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Types:
Thermodynamic systems are classified as:
• Open system
• Closed system
• Isolated system
• Open System:
Open System:
If the thermodynamic system has the capacity to exchange both matter and energy
with its surroundings, it is said to be an open system.
Example:
A pool filled with water, where the water can enter or leave the pool.
Closed System:
A system that has the ability to exchange only energy with its surroundings and
cannot exchange matter is known as a closed system.
Example:
When we boil water with a closed lid, the heat can exchange but matter cannot.
Isolated System:
It is one that cannot exchange either matter or energy with its surroundings.
Example:
A thermos flask is the best example of an
isolated system. A thermos flask is used
to keep things either cold or hot. Thus, a
thermos does not allow energy to
transfer.

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Related Terms Regarding Laws of Thermodynamics:
What is Heat?
Heat is the flow of energy from a high temperature to a low temperature.
What is temperature?
The degree of heat.
What is Enthalpy?
Enthalpy is the measurement of energy in a thermodynamic system.
Mathematically, the enthalpy, H, equals the sum of the internal energy, E, and the
product of the pressure, P, and volume, V, of the system.
H = E + PV
Where;
H = Enthalpy
E = Internal Energy
P = Pressure
V = Volume of System
What is Entropy?
The thermodynamic function is used to measure the randomness or disorder.
For example, the entropy of a solid, where the
particles are not free to move, is less than the
entropy of a gas, where the particles will fill the
container.

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What is thermal Equilibrium?
It is only concerned with one form of internal energy namely the Kinetic Energy (KE)
of the molecules.
What is Thermodynamic Equilibrium?
It is the state of maximum entropy.
The Laws of Thermodynamics:
• The laws of thermodynamics describe how the energy in a system change and
whether the system can perform useful work on its surroundings.
• Thermodynamics laws define fundamental physical quantities like energy,
temperature, and entropy. These thermodynamics laws represent how these
quantities behave under various circumstances.
Laws:
There are four laws of thermodynamics which are given below:
• Zeroth law of thermodynamics
• First law of thermodynamics
• Second law of thermodynamics
• Third law of thermodynamics
Zeroth Law of Thermodynamics:
It states that if two bodies are individually in equilibrium with a separate third body,
then the first two bodies are also in thermal equilibrium with each other.
First Law of Thermodynamics:
• It is also known as the law of conservation of energy, which states that energy
can neither be created nor destroyed, but it can be changed from one form to
another.

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• This law helps us understand that energy never
disappears or goes away, it only gets moved
around, or used in different ways.
Conservation:
Something which doesn't change.
Second Law of Thermodynamics:
The second law of thermodynamics states that the entropy in an isolated system
always increases.
Example: Scattered things in a room
Third Law of Thermodynamics:
The third law of thermodynamics states that the entropy of a system approaches a
constant value as the temperature approaches absolute zero.
Example:
The molecules within the steam move randomly. Therefore, it has high Entropy. If
these vapors are set for cooling this steam to below 100 degrees Celsius it will get
transformed into water, where the movement of the molecules will be restricted
resulting in a decrease in Entropy.

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The internal energy U of a system is the sum of the kinetic and potential energies of
its atoms and molecules. Recall that kinetic plus potential energy is called mechanical
energy.
ΔU=Q−W
Here ΔU is the change in internal energy U of the system. Q is the net heat transferred
into the system—that is, Q is the sum of all heat transferred into and out of the
system. (What do you think both symbols + and – are ok here?)
Example 1:
Calculating Change in Internal Energy: The Same Change in U is Produced by Two
Different Processes.
(a) Suppose there is a heat transfer of 40.00 J to a system, while the system does
10.00 J of work. Later, there is a heat transfer of 25.00 J out of the system while 4.00
J of work is done on the system. What is the net change in the internal energy of the
system?
(b) What is the change in internal energy of a system when a total of 150.00 J of heat
transfer occurs out of (from) the system and 159.00 J of work is done on the system?
Strategy
In part (a), we must first find the net heat transfer and network done from the given
information. Then the first law of thermodynamics (ΔU=Q−W) can be used to find the

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change in internal energy. In part (b), the net heat transfer and work done are given,
so the equation can be used directly.
Solution for (a)
The net heat transfer is the heat transfer into the system minus the heat transfer out
of the system, or
Q=40.00 J−25.00 J=15.00 J
Similarly, the total work is the work done by the system minus the work done on the
system, or
W=10.00 J−4.00 J=6.00 J
Thus, the change in internal energy is given by the first law of thermodynamics:
ΔU=Q−W=15.00 J−6.00 J=9.00 J
We can also find the change in internal energy for each of the two steps. First, consider
40.00 J of heat transfer in and 10.00 J of workout, or
ΔU1=Q1−W1=40.00 J−10.00 J=30.00 J
Now consider 25.00 J of heat transfer out and 4.00 J of work in, or
ΔU2=Q2−W2=−25.00 J−(−4.00 J) =−21.00 J
The total change is the sum of these two steps, or
ΔU=ΔU1+ΔU2=30.00 J+(−21.00 J) =9.00 J
Discussion on (a)
No matter whether you look at the overall process or break it into steps, the change
in internal energy is the same.

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Solution for (b)
Here the net heat transfer and total work are given directly to be Q=−150.00 JJ and
W=−159.00 J, so that
ΔU=Q−W=−150.00 J−(−159.00 J) =9.00 J
You are suggested to solve some more examples of heat transfer (as stated above) by
yourself by using any source.
Reversible and Irreversible Process:
Reversible Process:
A process that can be reversed without leaving any trace on the surroundings.

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• Reversible processes do not occur, and they are only idealizations of actual
processes.
• In a reversible process things happen very slowly, without any resisting force,
without any space limitation → everything happens in a highly organized way
(it is not physically possible ‐ it is an idealization).
Irreversible Process:
Processes that are not reversible are called irreversible.
Internally Reversible Process:
If no irreversibilities occur within the boundaries of the system. In these processes, a
system undergoes a series of equilibrium states.
Internally Reversible Process:
if no irreversibilities occur outside the system boundaries during the process.
Useful web link for heat, its units, and related terms:
(This link contains the contents we discussed in the lecture on Tuesday).
https://www.vedantu.com/physics/unit-of-heat