THERMODYNAMICS
INTRODUCTION:
Thermodynamics in physicsis a branch that deals
with heat, work and temperature, and their relation to
energy, radiation and physical properties of matter.
Thermodynamics is the study of the relationships
between heat, work, energy, and other thermodynamic
variables like temperature, pressure, and entropy. It
deals with the behaviour of macroscopic systems,
such as gases, liquids, and solids, and their
interactions with their surroundings.
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• Thermodynamics isnot concerned
about how and at what rate these
energy transformations are carried out.
It is based on the initial and final states
undergoing the change. It should also
be noted that Thermodynamics is a
macroscopic science. This means that
it deals with the bulk system and does
not deal with the molecular
constitution of matter.
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Basic Concepts ofThermodynamics
A thermodynamic system is a specific portion of matter with a definite boundary on which
our attention is focused. The system boundary may be real or imaginary, fixed or
deformable.
There are three types of systems:
• Isolated System – An isolated system cannot exchange energy and mass with its
surroundings. The universe is considered an isolated system.
• Closed System – Across the boundary of the closed system, the transfer of energy takes
place, but the transfer of mass doesn’t take place. Refrigerator, compression of gas in the
piston-cylinder assembly are examples of closed systems.
• Open System – In an open system, the mass and energy both may be transferred
between the system and surroundings. A steam turbine is an example of an open system.
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Thermodynamic Process
A systemundergoes a thermodynamic process when there is some energetic change within the
system that is associated with changes in pressure, volume and internal energy. There are four
types of thermodynamic processes that have their unique properties, and they are:
• Adiabatic Process – A process where no heat transfer into or out of the system occurs.
• Isochoric Process – A process where no change in volume occurs and the system does no
work.
• Isobaric Process – A process in which no change in pressure occurs.
• Isothermal Process – A process in which no change in temperature occurs.
A thermodynamic cycle is a process, or a combination of processes conducted such that the
initial and final states of the system are the same. A thermodynamic cycle is also known as
cyclic operation or cyclic processes
9.
Thermodynamic Equilibrium
At agiven state, all properties of a system have fixed values. Thus, if the value of even one property changes, the
system’s state changes to a different one. In a system that is in equilibrium, no changes in the value of properties
occur when it is isolated from its surroundings.
• When the temperature is the same throughout the entire system, we consider the system to be in thermal
equilibrium.
• When there is no change in pressure at any point of the system, we consider the system to be in mechanical
equilibrium.
• When the chemical composition of a system does not vary with time, we consider the system to be in chemical
equilibrium.
• Phase equilibrium in a two-phase system is when the mass of each phase reaches an equilibrium level.
A thermodynamic system is said to be in thermodynamic equilibrium if it is in chemical equilibrium, mechanical
equilibrium and thermal equilibrium and the relevant parameters cease to vary with time.
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Laws of thermodynamics
•The laws of thermodynamics are:
• First law of thermodynamics: Energy can neither be created nor be
destroyed, it can only be transferred from one form to another.
• Second law of thermodynamics: The entropy of any isolated system always
increases.
• Third law of thermodynamics: The entropy of a system approaches a
constant value as the temperature approaches absolute zero.
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Thermodynamic Equations:
The followingequations are used in thermodynamics:
The First Law of Thermodynamics: ΔU = Q - W
The Second Law of Thermodynamics: ΔS ≥ Q/T
The Third Law of Thermodynamics: S = 0 at absolute zero
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Zeroth Law ofThermodynamics
• The Zeroth law of thermodynamics 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.
• This means that if system A is in thermal
equilibrium with system C and system B is also
in equilibrium with system C, then system A and
B are also in thermal equilibrium.
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Types of Thermodynamics
Thermodynamicsis classified into the following four branches:
• Classical Thermodynamics
• Statistical Thermodynamics
• Chemical Thermodynamics
• Equilibrium Thermodynamics
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• Classical Thermodynamics
Inclassical thermodynamics, the behaviour of matter is analysed with a macroscopic approach. Units such
as temperature and pressure are taken into consideration, which helps the individuals calculate other
properties and predict the characteristics of the matter undergoing the process.
• Statistical Thermodynamics
In statistical thermodynamics, every molecule is under the spotlight, i.e., the properties of every molecule
and how they interact are taken into consideration to characterise the behaviour of a group of molecules.
• Chemical Thermodynamics
Chemical thermodynamics is the study of how work and heat relate to each other in chemical reactions and
in changes of states.
• Equilibrium Thermodynamics
Equilibrium thermodynamics is the study of transformations of energy and matter as they approach the
state of equilibrium.
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Thermodynamic Properties
• Thermodynamicproperties are defined as characteristic features of a system,
capable of specifying the system’s state. Thermodynamic properties may
be extensive or intensive.
• Intensive properties are properties that do not depend on the quantity of
matter. Pressure and temperature are intensive properties.
• In the case of extensive properties, their values depends on the mass of the
system. Volume, energy, and enthalpy are extensive properties.
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Enthalpy
Enthalpy is athermodynamic property that measures the total energy of a system, including
both its internal energy and the energy required to create its volume and pressure. Enthalpy is
a state function, meaning that it depends only on the current state of the system and not on
how the system arrived at that state.
• Enthalpy Equation:
The enthalpy of a system can be calculated using the following equation:
H = U + PV
Where:
H = Enthalpy
U = Internal Energy
P = Pressure
V = Volume
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• If thepressure and volume of the system are constant, then the change in
enthalpy can be calculated using the following equation:
ΔH = ΔU + PΔV
• If the reaction is carried out at constant pressure, the change in enthalpy is
also equal to the heat absorbed or released by the system:
ΔH = q
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Enthalpy changes canbe classified as either exothermic or endothermic
depending on whether the reaction releases or absorbs heat, respectively.
• Exothermic reaction: In an exothermic reaction, the reactants have a higher
enthalpy than the products. As the reaction proceeds, energy is released in the
form of heat. The enthalpy change (ΔH) for an exothermic reaction is negative.
Examples of exothermic reactions include combustion reactions, where a fuel
(such as wood or gasoline) reacts with oxygen to produce heat and light energy.
• Endothermic reaction: In an endothermic reaction, the reactants have a lower
enthalpy than the products. As the reaction proceeds, energy is absorbed in the
form of heat. The enthalpy change (ΔH) for an endothermic reaction is positive.
Examples of endothermic reactions include the melting of ice, where heat energy
is required to convert solid ice into liquid water.
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It's important tonote that the
sign of the enthalpy change
(positive or negative) indicates
the direction of the energy
flow, not the magnitude. The
magnitude of the enthalpy
change depends on the quantity
of reactants and products and
the specific conditions under
which the reaction occurs.
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• Enthalpy isoften used in chemical and physical processes to describe the
energy transfer that occurs during a reaction or a phase change. For example,
the enthalpy of combustion is the energy released when a substance is burned
in oxygen.
• Enthalpy is related to other thermodynamic properties, such as entropy and
Gibbs free energy, through various thermodynamic equations. One of the
most important of these equations is the first law of thermodynamics, which
states that the change in internal energy of a system is equal to the heat added
to the system minus the work done by the system.
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Enthalpy has numerouspractical applications, including:
• Chemical reactions: Enthalpy is used to determine the heat of reaction for chemical
reactions.
• Phase transitions: Enthalpy is used to determine the heat required to change the phase of a
substance (e.g., from a solid to a liquid or a liquid to a gas).
• Heat transfer: Enthalpy is used to determine the amount of heat required to transfer energy
from one system to another.
• Combustion: Enthalpy is used to determine the heat released or absorbed during combustion
reactions.
Enthalpy is an important thermodynamic property that plays a critical role in many natural and
industrial processes. Its applications range from the study of chemical reactions to the design of
power plants and engines.
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Entropy
• Entropy isa fundamental concept in thermodynamics, information theory,
and probability theory, among other fields. It is a measure of the degree of
disorder or randomness in a system or a set of data.
• In thermodynamics, entropy is defined as the measure of the amount of
energy in a system that is unavailable for work. It is often denoted by the
symbol S and is measured in units of joules per kelvin (J/K). The second law
of thermodynamics states that the entropy of an isolated system will tend to
increase over time, meaning that the system will tend to become more
disordered and less useful for doing work.
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Entropy has manyapplications in science, engineering, and technology. Here are a few examples:
• Thermodynamics: Entropy is a key concept in thermodynamics and is used to describe the
behavior of physical systems. It helps to explain phenomena such as heat transfer, phase
transitions, and chemical reactions.
• Information Theory: Entropy is used in information theory to measure the amount of
uncertainty or randomness in a set of data. It is used in data compression, where it helps to
identify patterns and redundancies in data that can be eliminated to reduce the amount of storage
or bandwidth required.
• Statistical Mechanics: Entropy is used in statistical mechanics to describe the behavior of large
systems of particles. It helps to predict the properties of materials and their response to changes
in temperature, pressure, or other external factors.
• Artificial Intelligence: Entropy is used in machine learning and artificial intelligence to
measure the uncertainty or randomness in the output of a model. It is used to evaluate the
performance of models and to select the most appropriate model for a given task
• Biology: Entropy is used in biology to describe the complexity and diversity of biological
systems. It helps to explain phenomena such as evolution, gene expression, and protein folding.
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Free energy
• Inthermodynamics, free energy refers to the energy available to do useful
work in a system. It is a measure of the energy that can be extracted from a
system and used to perform work, such as moving a piston or generating
electricity.
• The free energy of a system is also known as the Gibbs free energy, named
after the American physicist Josiah Willard Gibbs.
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The Gibbs freeenergy
• The Gibbs free energy is a measure of the system's ability to do work and is related to the
spontaneity of a process. A decrease in the Gibbs free energy of a system during a process
indicates that the process is spontaneous and can occur without the input of external energy.
Conversely, an increase in Gibbs free energy indicates that the process is non-spontaneous
and requires external energy to occur.
It is denoted by the symbol G and is defined as the difference between the enthalpy (H) of a
system and its entropy (S), multiplied by the absolute temperature (T):
G = H - TS
Where:
G = Gibbs free energy
H = Enthalpy (the total heat content of the system)
S = Entropy (the degree of disorder of the system)
T= Absolute temperature
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Coupling reactions
• Couplingreactions in thermodynamics refer to a process where the energy
released by one reaction is used to drive another reaction, allowing both
reactions to occur simultaneously.
• In a coupled reaction, the energy released from an exothermic reaction (one
that releases energy) is used to drive an endothermic reaction (one that absorbs
energy). This coupling of reactions allows for a net decrease in the overall free
energy of the system, making the coupled reaction more favorable than either
reaction alone.
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• For example,the synthesis of ATP (adenosine triphosphate) from ADP
(adenosine diphosphate) and inorganic phosphate (Pi) is a coupled reaction
that is essential for energy transfer in living organisms. The reaction is
coupled with the exothermic breakdown of glucose, which releases energy
that is used to drive the endothermic synthesis of ATP. This coupling of
reactions allows for the net transfer of energy from glucose to ATP, which can
then be used to power cellular processes.
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Principle of CouplingReaction
• The principle of coupling reactions is based on the fact that some reactions release
energy, while others require energy to occur. By combining these two reactions in a
coupled system, the energy released by the exothermic reaction can be used to
drive the endothermic reaction, allowing both reactions to occur simultaneously.
• In order for a coupled reaction to occur, the two reactions must be
thermodynamically compatible. This means that the overall free energy change of
the coupled reaction must be negative, indicating that the reaction is spontaneous
and can occur without the need for external energy.
• In other words, The principle of coupled reactions in thermodynamics is based on
using the energy released from an exothermic reaction to drive an endothermic
reaction, allowing both reactions to occur simultaneously and efficiently transfer
and use energy.
• Thermodynamics playsa significant role in various healthcare applications,
contributing to the diagnosis, treatment, and overall functioning of medical
devices. Here are several ways in which thermodynamics is applied in
healthcare:
• 1. Medical Imaging (MRI): MRI technology relies on the principles of
thermodynamics to detect and analyze signals from hydrogen atoms in the
body's tissues. Thermodynamic properties of tissues influence image contrast,
aiding in the diagnosis of various medical conditions.
• 2. Cryopreservation: Cryogenic Storage: Thermodynamics principles are
applied in cryopreservation to store biological materials (such as cells,
tissues, and embryos) at ultra-low temperatures, ensuring their viability for
transplantation and research.
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• 3. HeatTherapy: Hyperthermia Treatment: Controlled application of heat
to body tissues can be used in cancer therapy. Thermodynamics principles are
used to calculate the appropriate heat levels for specific tissues, ensuring
targeted therapy to destroy cancer cells.
• 4. Medical Devices: Thermoregulation Devices: Devices like incubators for
premature babies and warming blankets utilize thermodynamics to regulate
and maintain body temperature, especially in critical care situations. Dialysis
Machines: Thermodynamics principles are employed in the design of dialysis
machines, ensuring efficient removal of waste products from the blood during
kidney dialysis processes.
• 5. Respiratory Devices: Ventilators: Thermodynamics principles guide the
functioning of ventilators, ensuring the precise mixture of oxygen and other
gases for patients with respiratory issues.
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• 6. DiagnosticTools: Thermometers: Various types of thermometers,
including infrared thermometers and thermocouples, are based on
thermodynamics principles, providing accurate temperature measurements
used in medical diagnosis.
• 7. Biomedical Research: Protein Folding Studies: Thermodynamics
principles are crucial in understanding the folding and stability of proteins, a
fundamental aspect of molecular biology and drug discovery. Calorimetry:
Calorimetric techniques, such as differential scanning calorimetry (DSC),
measure heat changes in biochemical reactions, aiding in drug design and
biomolecular studies.
• 8. Pharmaceuticals: Freeze-Drying (Lyophilization): Thermodynamics
principles guide the freeze-drying process, preserving pharmaceuticals and
vaccines by removing water content without affecting their efficacy. Drug
Delivery Systems: Thermodynamics plays a role in the design of drug
delivery systems, ensuring controlled release and stability of medications
within the body.
#14 Consider two cups A and B, with boiling water. When a thermometer is placed in cup A, it gets warmed up by the water until it reads 100 °C. When it reads 100 °C, we say that the thermometer is in equilibrium with cup A. When we move the thermometer to cup B to read the temperature, it continues to read 100 °C. The thermometer is also in equilibrium with cup B. By keeping in mind the zeroth law of thermodynamics, we can conclude that cup A and cup B are in equilibrium with each other.
The zeroth law of thermodynamics enables us to use thermometers to compare the temperature of any two objects that we like.
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