THERMODYNAMICS

Mr. NITIN SINGHAL

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 What is Thermodynamics?
❖ Thermodynamics is the
fascinating branch of science
which deals with energy transfer
and its effect on the state or
condition of a system.
❖ Energy transformations – mostly
involve heat and work movements.
❖ The Fundamental law is the
conservation of energy principle:
energy cannot be created or
destroyed, but can only be
transformed from one form to
another.

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 System, surroundings and boundary

❖ System: A quantity of matter or a

region in space chosen for study.

❖ Surroundings: The mass or region

outside the system

❖ Boundary: The real or imaginary

surface that separates the system
from its surroundings.

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 Type of system
(isolated system)

❖ Isolated system – neither

mass nor energy can cross
the selected boundary

❖ Example (approximate): coffee in

a closed, well-insulated thermos
bottle

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 Type of system
(Closed system)

❖ Closed system – only energy

can cross the selected
boundary

❖ Examples: a tightly capped cup of

coffee

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 Type of system
(Open system)

❖ Open system – both mass and

energy can cross the selected
boundary

❖ Example: an open cup of coffee

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 Properties of a system
Properties of a system is a measurable characteristic of a system that is
in equilibrium.
Properties may be intensive or extensive.

❖ Intensive – Are independent of the amount of mass:

e.g: Temperature, Pressure, and Density,

❖ Extensive – varies directly with the mass

e.g: mass, volume, energy, enthalpy

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 Properties of a system
Specific properties – The ratio of any extensive property of a system to that of

the mass of the system is called an average specific value of that property (also

known as intensives property)

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 State, Equilibrium and Process

❖ State – a set of properties that describes the conditions of a

system. Eg. Mass m, Temperature T, volume V

❖ Thermodynamic equilibrium -
system that maintains thermal,
mechanical, phase and chemical
equilibriums.

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 State, Equilibrium and Process
❖ Process – change from one
equilibrium state to another.

Process Property held

constant
isobaric pressure
isothermal temperature
isochoric volume
isentropic entropy

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 State, Equilibrium and Process
The prefix iso- is often used to designate a process for which a particular property
remains constant.

Isobaric process: A process during which the pressure P remains constant.

Pressure is Constant (ΔP = 0)

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 State, Equilibrium and Process
Isochoric (or isometric) process: A process during which the specific volume v
remains constant

Process Property held

constant
Isothermal process: A process during
which the temperature T remains
isobaric pressure
constant. isothermal temperature
.
isochoric volume
isentropic entropy
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 Types of Thermodynamics Processes
❖ Cyclic process - when a system in a given initial
state goes through various processes and finally
return to its initial state, the system has undergone
a cyclic process or cycle.

❖ Reversible process - it is defined as a process

that, once having take place it can be reversed. In
doing so, it leaves no change in the system or
boundary.

❖ Irreversible process - a process that cannot

return both the system and surrounding to their
original conditions

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 Types of Thermodynamics Processes
❖ Adiabatic process - a process that has no heat transfer
into or out of the system. It can be considered to be
perfectly insulated.
❖ Isentropic process - a process where the entropy of the
fluid remains constant.

❖ Polytropic process - when a gas undergoes a reversible

process in which there is heat transfer, it is represented
with a straight line, PVn = constant.
❖ Throttling process - a process in which there is no
change in enthalpy, no work is done and the process is
adiabatic.

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 Zeroth Law of Thermodynamics

“ If two bodies are in thermal equilibrium with a third

body, there are also in thermal equilibrium with each
other.”

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 Thermodynamic equilibrium
• A system is said to be in thermodynamic equilibrium which is incapable of

any spontaneous change of its macroscopic properties (p, v, t) and it is in

complete balance with its surroundings.

• A system will be in thermodynamic equilibrium if it satisfies the condition

of mechanical, thermal and chemical equilibrium

1. Mechanical equilibrium :- No unbalance forces

2. Thermal Equilibrium :- Uniformity of temp. inside with surrounding

3. Chemical Equilibrium :- Absence of any chemical reaction

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 Quasi Static Process / Reversible
• A quasi static process is defined as a process in which the properties of the

system depart infinitesimally (extremely small) from the thermodynamic equilibrium

path

• If the properties of the system has finite departures from thermodynamic

equilibrium path the process is said to be non quasi static

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 Condition for reversible process are
1. No Friction

2. Heat transfer is through infinitely temperature difference.

3. There are no spontaneous changes in the system.

• All processes in nature are irreversible.

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 Heat
• Heat is the form of energy which transfer without transfer of mass, from one

body to another body (or between system and surroundings) from higher

temperature to lower temperature by virtue of temperature difference between

two bodies.

• Abbreviated as ‘Q’ and Unit is J (Joule)

• Heat Addition into system :- Positive ( +Q)

• Heat Rejection from system :- Negative (-Q)

• Extensive Property and Path Function (Inexact Differential)

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 Difference between heat and work
1. Heat can only transfer when there is difference of temperature between the

system and surrounding, while work transfer can take place even without the

change in temperature

2. In constant volume process though work can not take place, however

heat can be transferred.

3. In case of work transfer, its sole effect could be raising or lowering a weight

in the surrounding but in case of heat transfer other effects are also observed.

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 Enthalpy
• It is total energy of the system

• Specific Enthalpy,

• U, p, V are point function, so H is point function and property of system

• Unit of Enthalpy (H) is kJ

• Unit of Specific Enthalpy (h) is kJ/kg

H = U + pV

h = u + pv

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 THANK YOU

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