Laws of thermodynamics

1. INTRODUCTIONINTRODUCTION
Topic :: Laws of ThermodynamicsLaws of Thermodynamics
FARAZ AHMED (14EL-42)
QUEST NAWABSHSH

2. ThermodynamicsThermodynamics
 Thermodynamics is the branch of physics that is
built upon the fundamental laws that heat and
work obey.
 Thermodynamics is the study of the effects of
work, heat, and energy on a system.
 Thermodynamics is only concerned with
macroscopic (large-scale) changes and
observations.
 Thermodynamics is the science of the
relationship between heat, work and systems
that analuze energy processes.

3. Law of ThermodynamicsLaw of Thermodynamics
•The Zeroth law of Thermodynamics.
• The First Law of Thermodynamics.
•The Second Law of Thermodynamics
•The Third Law of Thermodynamics

4. The Zeroth Law of ThermodynamicsThe Zeroth Law of Thermodynamics
If object A is in thermal
equilibrium with object C,
and object B is separately in
thermal equilibrium with
object C, then objects A and
B will be in thermal
equilibrium if they are
placed in thermal contact.

5. The First Law of ThermodynamicsThe First Law of Thermodynamics
 The first law of thermodynamics, also known as Law of
Conservation of Energy,
 Energy can neither be created nor destroyed; it can only
be transferred or changed from one form to another
 A way of expressing the first law of thermodynamics is
that any change in the internal energy(∆E) of a system is
given by the sum of the heat (Q) that flows across its
boundaries and the work (W) done on the system by the
surroundings:
 ΔE = Q + W

6. Application Of First Law of ThermodynamicsApplication Of First Law of Thermodynamics
Isobaric – constant pressure
Isochoric – constant volume
Isothermal – constant temperature
Adiabatic – no heat transferred

7. IIsobaric processsobaric process
An isobaric process is a constant pressure
process.
ΔU, W, and Q are generally non-zero.
work done by an ideal gas is
W = P·ΔV
Water boiling in a saucepan is an example
of an isobaric process

8. IIsochoric processsochoric process
An isochoric process is a constant volume
process.
When the volume of a system doesn’t
change, it will do no work on its
surroundings. W = 0
ΔU = Q
Heating gas in a closed container is an
example of isochoric process

9. Isothermal processIsothermal process
An isothermal process is a constant
temperature process.
Any heat flow into or out of the system
must be slow enough to maintain thermal
equilibrium
For ideal gases, if ΔT is zero, ΔU = 0
Therefore, Q = W
 Any energy entering the system (Q) must leave
as work (W)

10. Adiabatic processAdiabatic process
 An adiabatic process no heat transfer or leave the
system i-e Q=0
• Therefore ΔU = – W
 When a system expands adiabatically, W is positive (the
system does work) so ΔU is negative, i-e W = - ΔU
 When a system compresses adiabatically, W is negative
(work is done on the system) so ΔU is positive.
- W = ΔU

11. The Second Law of ThermodynamicsThe Second Law of Thermodynamics
 Heat cannot be converted fully to work.
 Heat is transferred spontaneously only from a high
temperature body to a low temperature body.
(Spontaneously: without applying external work).
 The entropy of an isolated system never decreases.
 It is impossible to construct a heat engine which is 100%
efficient. Thus, a heat engine can convert some of input
heat into useful work, but the rest must be exhausted as
waste heat.

12. The Third Law of ThermodynamicsThe Third Law of Thermodynamics
 "The entropy of a pure perfect crystal is zero (0) at zero
Kelvin (0 K).
 the temperature of a system approaches absolute zero,
its entropy approaches a constant (for pure perfect
crystals, this constant is zero).

13. Pure Perfect Crystal:
A pure perfect crystal is
one in which every
molecule is identical
Entropy can become zero.
Non Pure Crystal:
A pure perfect crystal is
one in which every
molecule is not identical
Entropy cannot become
zero.

14. EXAMPLEEXAMPLE
 Water in gas form has molecules that can move around very freely.
Water vapor has very high entropy (randomness).
 As the gas cools, it becomes liquid. The liquid water molecules can
still move around, but not as freely. They have lost some entropy.
 When the water cools further, it becomes solid ice. The solid water
molecules can no longer move freely, but can only vibrate within the
ice crystals. The entropy is now very low.
 As the water is cooled more, closer and closer to absolute zero, the
vibration of the molecules diminishes.
 If the solid water reached absolute zero, all molecular motion would
stop completely. At this point, the water would have no entropy
(randomness) at all.