explains about four laws of thermodynamics and their consequences

1. Laws of thermodynamics and
their significance
Mrs.P.Kanmani, M.Sc., M.Phil.,
Assistant Professor of Physics.

2. Thermodynamics
• The word thermodynamics comes from the Greek
words thermos which means heat and dynamis which means
power.
• Thermodynamics is a branch of physics which deals with the
energy and work of a system i.e it studies the movement of
energy and how energy creates movement.
• Thermodynamics deals only with the large scale response of
a system which we can observe and measure in experiments.

3. Laws of thermodynamics
• There are four laws of thermodynamics, and they are some of
the most important laws in all of Physics. The laws are as
follows
– Zeroth law
– First law
– Second law
– Third law

4. Zeroth law
• The Zeroth Law of Thermodynamics states that if two bodies
are each in thermal equilibrium with some third body, then
they are also in equilibrium with each other.
• By the term thermal equilibrium it is meant that, there will be
no heat transfer when the systems in thermal equilibrium are
brought into contact with each other.

5. Significance of Zeroth law
• In essence, the three bodies are all at the same temperature.
• The Zeroth Law establishes that temperature is a fundamental
and measurable property of matter.
• Temperature, defines the direction of heat flow, and it does
not depend directly on the amount of energy that’s involved.

6. First law
• 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.

7. First law
• Mathematically, this is represented as
ΔU=q + w
ΔU is the total change in internal energy of a system
(The internal energy of a system is the sum of the kinetic and
potential energies of its atoms and molecules.)
q is the heat exchanged between the system and its
surroundings, and
w is the work done by or on the system. (w is negative if work
is done by the system and positive if work is done onto the
system.)

8. First law
• Work is also equal to the negative external pressure on the
system multiplied by the change in volume:
w=−pΔV
• where p is the external pressure on the system, and ΔV is the
change in volume.
• The internal energy of a system would decrease if the system
gives off heat or does work. Therefore, internal energy of a
system increases when the heat increases (this would be done
by adding heat into a system). The internal energy would also
increase if work were done onto a system.

9. First law
• Any work or heat that goes into or out of a system changes the
internal energy. However, since energy is never created nor
destroyed, the change in internal energy always equals zero. If
energy is lost by the system, then it is absorbed by the
surroundings. If energy is absorbed into a system, then that energy
was released by the surroundings:
ΔUsystem=−ΔUsurroundings
where ΔUsystem is the total internal energy in a system, and
ΔUsurroundingsis the total energy of the surroundings.

10. Significance of first law
• The first law of thermodynamics concludes that,
– To produce a definite amount of work, one must expend an equal
amount of energy. This is the assertion that the perpetual machines of
the first kind do not exist.
– The total amount of energy of an isolated system remains constant, it
may change from on form to another.

11. Significance of first law
– The energy of the universe remains constant.
– For a system in contact with the surroundings, the sum of the energies
of the system and its surroundings remains constant, however
differently it may be shared between the two.
• First law allows us to calculate internal energy of a system
using macroscopic parameters.

12. Second law
• The Second Law of Thermodynamics is about the quality of
energy.
• It states that as energy is transferred or transformed, more
and more of it is wasted.
• The Second Law also states that there is a natural tendency of
any isolated system to degenerate into a more disordered
state.

13. Second law
• At a very microscopic level, it can be stated that if a system is
isolated, any natural process in that system progresses in the
direction of increasing disorder, or entropy, of the system.

14. Significance of second law
• Second Law explains that, it is impossible to convert heat
energy to mechanical energy with 100 percent efficiency.
• After the process of heating a gas to increase its pressure to
drive a piston, there is always some leftover heat in the gas
that cannot be used to do any additional work.
• This waste heat must be discarded by transferring it to a heat
sink. In the case of a car engine, this is done by exhausting the
spent fuel and air mixture to the atmosphere.

15. Significance of second law
• When a hot and a cold body are brought into contact with each
other, heat energy will flow from the hot body to the cold body
until they reach thermal equilibrium, i.e., the same temperature.
• However, the heat will never move back the other way; the
difference in the temperatures of the two bodies will never
spontaneously increase.
• Moving heat from a cold body to a hot body requires work to be
done by an external energy source.

16. Significance of second law
• The Second Law indicates processes that involve the transfer
or conversion of heat energy, are irreversible because they all
result in an increase in entropy.
one of the most consequential implications of the Second
Law, is that it gives us the thermodynamic arrow of time.

17. Significance of second law
• The Second Law also predicts the end of the universe.
• It implies that the universe will end in a ‘heat death’ in which
everything is at the same temperature.
• This is the ultimate level of disorder; if everything is at the
same temperature, no work can be done, and all the energy
will end up as the random motion of atoms and molecules.

18. Third law
• The third law of thermodynamics states that the entropy of a
system approaches a constant value as the temperature
approaches absolute zero.
• The entropy of a system at absolute zero is typically zero.
• Specifically, the entropy of a pure crystalline substance
(perfect order) at absolute zero temperature is zero.

19. Significance of Third law
• At zero temperature, the system must be in a state with the
minimum thermal energy.(Practically no system can reach
absolute zero)
• For the entropy at absolute zero to be zero, the magnetic
moments of a perfectly ordered crystal must themselves be
perfectly ordered.
• Molecules near these temperatures have been called the fifth
state of matter and known as Bose–Einstein condensates.

20. Significance of Third law
• Super fluidity and superconductivity occur at these
temperatures.
• Technically, temperatures as low as 100 pK have been
obtained in the laboratory and temperatures as low as 3 K
observed experimentally in space.