2. What is Thermodynamics?
Thermodynamics deals with the transfer of energy
from one place to another and from one form to
another. The key concept is that heat is a form of
energy corresponding to a definite amount of
mechanical work.
OR
The scientific study of the relations between heat
and other forms of energy.
3. Laws of thermodyanmics
ZEROTH LAW OF THERMODYNAMICS
The Zeroth Law of Thermodynamics states that if two
systems are in thermodynamic equilibrium with a third
system, the two original systems are in thermal equilibrium
with each other. Basically, if system A is in thermal
equilibrium with system C and system B is also in thermal
equilibrium with system C, system A and system B are in
thermal equilibrium with each other.
5. Laws of thermodyanmics
1ST LAW OF THERMODYNAMICS
The First Law of Thermodynamics states that energy can be converted from
one form to another with the interaction of heat, work and internal energy,
but it cannot be created nor destroyed, under any circumstances.
Euniv=Esys+Esurr
the total amount of energy within the universe does not change, one can set
a change in energy of the system and surroundings to equal :-
ΔEsys+ΔEsurr=0
7. Laws of thermodyanmics
2ND LAW OF THERMODYNAMICS
The Second Law of Thermodynamics states that the state of
entropy of the entire universe, as an isolated system, will
always increase over time. The second law also states that
the changes in the entropy in the universe can never be
negative.
HOT HEAT COLD
8. Laws of thermodyanmics
KELVIN PLANK STATEMENT
No process is possible whose sole result is the absorption of heat
from a reservoir and the complete conversion of the heat into
work
CLAUSIS STATEMEMT
No process is possible whose sole result is the transfer of heat
from a colder object to a hotter object.
9. Laws of thermodyanmics
3RD LAW OF THERMODYNAMICS
The third law of thermodynamics states that the entropy of a perfect
crystal at a temperature of zero Kelvin (absolute zero) is equal to zero.
•At a temperature of zero Kelvin, the following phenomena can be
observed in a closed system:
•The system does not contain any heat.
•All the atoms and molecules in the system are at their lowest
energy points.
10. WHAT IS ENTROPY?
The concept of entropy basically talks about the spontaneous
changes that occur in the everyday phenomenon or the tendency of
the universe towards disorder.
Generally, entropy is defined as a measure of randomness or
disorder of a system.
The statistical definition which was developed at a later stage
fstageocused on the thermodynamic properties which were defined
in terms of the statistics of the molecular motions of a system.
Entropy is a measure of the molecular disorder.
11. Properties of entropy
•It is a thermodynamic function.
•It is a state function. It depends on the state of the system and not
the path that is followed.
•It is represented by S but in the standard state, it is represented by
S°.
•It’s SI unit is J/Kmol.
•It’s CGS unit is cal/Kmol.
•Entropy is an extensive property which means that it scales with the
size or extent of a system.
12. Heat capacity
Heat capacity is the heat required to increase an object temperature
by one degree. Heat gain or loss results in changes in temperature,
state, and performance of the work. Heat is a transfer of energy. The
heat capacity of a defined object is usually expressed in joules or
calories and temperature in Kelvin or Celsius.
The heat Capacity formula is expressed as the product of mass,
specific heat, and change in the temperature which is mathematically
given as:
Q = mcΔT
13. WHAT ARE phonons?
Phonon, in condensed-matter physics a unit of vibrational energy
that arises from oscillating atoms within acrystal
Any solid crystal, such as ordinary table salt (sodium chloride),
consists of atoms bound into a specific repeating three-
dimensional spatial pattern called a lattice. Because the atoms
behave as if they are connected by tiny springs, their own thermal
energy or outside forces make the lattice vibrate. This generates
mechanical waves that carry heat and sound through the material.
14. WHAT ARE phonons?
A packet of these waves can travel throughout the crystal with a
definite energy and momentum, so in quantum mechanical terms
the waves can be treated as a particle, called a phonon. A phonon
is a definite discrete unit or quantum of vibrational mechanical
energy, just as a photon is a quantum of electromagnetic or light
energy.
15. Debye’s law
A theory of the specific heat capacity of solids put forward by Peter
Debye in 1912, in which it was assumed that the specific heat is a
consequence of the vibrations of the atoms of the lattice of the
solid.
16. Debye’s law
Energy of system = Phonon Energy x
Average number of phonons x number
of modes
Debye postulated that there is a continuous range of frequencies
that cuts off at a maximum frequency νD, which is characteristic of
a particular solid. The theory leads to the conclusion that the
specific heat capacity of solids is proportional to T3, where T is the
thermodynamic temperature. This result is in very good agreement
with experiment at low temperatures.
