Laws of thermodynamics
Fundamental laws that helps you to
get better understanding with
physics concepts
We have four laws of thermodynamics, which
define fundamental physical quantities i.e.,
temperature,
energy,
and
entropy
that
characterize thermodynamic systems and their
behaviour under various circumstances.
They are
1. Zeroth law of thermodynamics
2. First law of thermodynamics
3. Second law of thermodynamics
4. Third law of thermodynamics
Zeroth law of thermodynamics
•
If two systems are in thermal equilibrium
with a third system, they must be in
thermal equilibrium with each other.
•
This law describes an empirical parameter,
the temperature, as a property of a system
such that systems in thermal equilibrium
with each other have the same
temperature.
First law of thermodynamics
• The increase in internal energy of a closed system is
equal to the heat supplied to the system minus work
done by it.
• First law of thermodynamics is also known as the
law of conservation of energy.
• This states that energy can be neither created nor
destroyed. However, energy can change forms, and
energy can flow from one place to another. The
total energy of an isolated system does not
change.
• dUsystem=Q - W
First Law includes several principles
• The law of conservation of energy.
• The concept of internal energy and its
relationship to temperature.
• The flow of heat is a form of energy
transfer.
• Work is a process of transferring energy to or
from a system.
Combining these principles leads to one
traditional statement of the first law of
thermodynamics:
It is not possible to construct a machine which will
perpetually output work without an equal amount
of energy input to that machine.
Or more briefly, a perpetual motion machine is
impossible.
Second law of thermodynamics
•
The entropy of any isolated system almost never
decreases. Such systems spontaneously evolve
towards thermodynamic equilibrium that is the
state of maximum entropy of the system.
Equivalently, perpetual motion machines of the
second kind are impossible.
•
According to this law, in a reversible heat transfer,
an element of heat transferred, δQ, is the product
of the temperature (T) and its entropy (S)
•
dQ = TdS
The 2nd Law can also be stated that heat flows
spontaneously from a hot object to a cold object
(spontaneously means without the assistance of
external work)
Third law of thermodynamics
• The entropy of a system approaches a constant value
as the temperature approaches absolute zero.
• At zero temperature the system must be in a state with
the minimum thermal energy. This statement holds true if
the perfect crystal has only one state with minimum
energy. Entropy is related to the number of possible
microstates according to:
S = kBln Ω
Where S is the entropy of the system, kB Boltzmann's
constant, and Ω the number of microstates
At absolute zero there is only 1 microstate possible (Ω=1
as all the atoms are identical for a pure substance and
as a result all orders are identical as there is only one
combination) and ln(1) = 0.
• A more general form of the third law that applies to a
systems such as a glass that may have more than one
minimum microscopically distinct energy state, or may
have a microscopically distinct state that is "frozen in"
though not a strictly minimum energy state and not
strictly speaking a state of thermodynamic equilibrium,
at absolute zero temperature:
• The entropy of a system approaches a constant value
as the temperature approaches zero.
• The constant value (not necessarily zero) is called the
residual entropy of the system.
Thank You