THERMODYNAMICS

BY Mohammed Fahaad
Class:11B

What is Thermodynamics?
Thermodynamics in physics is a branch that deals with heat, work and
temperature, and their relation to energy, radiation and physical properties of
matter.
To be specific, it explains how thermal energy is converted to or from other
forms of energy and how matter is affected by this process. Thermal energy is
the energy that comes from heat. This heat is generated by the movement of tiny
particles within an object, and the faster these particles move, the more heat is
generated.

.
Thermodynamics is not 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.

Thermodynamics Timeline
Distinction Between Mechanics and Thermodynamics
The distinction between mechanics and thermodynamics is worth noting. In
mechanics, we solely concentrate on the motion of particles or bodies under the
action of forces and torques. On the other hand, thermodynamics is not
concerned with the motion of the system as a whole. It is only concerned with
the internal macroscopic state of the body.

Different Branches of Thermodynamics

Thermodynamics is classified into the following four branches:

 Classical Thermodynamics
 Statistical Thermodynamics
 Chemical Thermodynamics
 Equilibrium Thermodynamics

Classical Thermodynamics
In classical 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.

Basic Concepts of Thermodynamics – Thermodynamic Terms

System
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.

Thermodynamic Process

A system undergoes 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.

Thermodynamic Properties
Thermodynamic properties 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.

What is Enthalpy?
Enthalpy is the measurement of energy in a thermodynamic system. The
quantity of enthalpy equals the total heat content of a system, equivalent to the
system’s internal energy plus the product of volume and pressure.
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

What is Entropy?
Entropy is a thermodynamic quantity whose value depends on the physical state or condition
of a system. In other words, it is a thermodynamic function 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.
Laws of Thermodynamics
Thermodynamics laws define the fundamental physical quantities like
energy, temperature and entropy that characterize thermodynamic
systems at thermal equilibrium. These thermodynamics laws represent
how these quantities behave under various circumstances.

How many laws of thermodynamics are there?

There are four laws of thermodynamics and are given below:

 Zeroth law of thermodynamics

 First law of thermodynamics

 Second law of thermodynamics

 Third law of thermodynamics

In the next few sections, we will discuss each of the laws of

thermodynamics in detail.

Zeroth Law of Thermodynamics

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.
An example demonstrating the Zeroth Law

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.

First Law of Thermodynamics

First law of thermodynamics, also known as the law of conservation
of energy, states that energy can neither be created nor destroyed, but
it can be changed from one form to another.

First Law Of Thermodynamics Examples:

  Plants convert the radiant energy of sunlight to chemical energy through
photosynthesis. We eat plants and convert the chemical energy into
kinetic energy while we swim, walk, breathe, and scroll through this
page.
 Switching on light may seem to produce energy, but it is electrical energy
that is converted.

Second Law of Thermodynamics

Second law of thermodynamics states that the entropy in an isolated system
always increases. Any isolated system spontaneously evolves towards thermal
equilibrium—the state of maximum entropy of the system.
The entropy of the universe only increases and never decreases. Many
individuals take this statement lightly and for granted, but it has an extensive
impact and consequence.

Third Law of Thermodynamics

Third law of thermodynamics states that the entropy of a system
approaches a constant value as the temperature approaches absolute
zero.

Thermodynamics – Summary and Overview

→ In simple terms, thermodynamics deals with the transfer of energy
from one form to another.
→ 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.
 Zeroth law of thermodynamics: If two thermodynamic systems are in thermal
equilibrium with a third system separately, then they are in thermal equilibrium with
each other.
→ Entropy is the measure of the number of possible arrangements
the atoms in a system can have.
→ Enthalpy is the measurement of energy in a thermodynamic
system.