Entropy

1. SEMINAR
ON
ENTROPY

2. CONTENTS
• INTRODUCTION
• VARIOUS TYPE OF DISORDER
• EXAMPLES OF DISORDER
• DEFINITION AND EXPRESSION OF ENTROPY
• IMPORTANCE OF ENTROPY IN GEOCHEMICAL
THERMODYNAMICS
• APPLICATION OF ENTROPY
• CONCUSION
• REFERENCE

3. INTRODUCTION
What is entropy?
 The word entropy is sometimes confused with energy.
Although they are related quantities, they are distinct.
 or energy measures the capability of an object or system
to do work.
 on the other hand, is a measure of the "disorder" of a
system. What "disorder refers to is really the number of
different microscopic states a system can be in, given that the
system has a particular fixed composition, volume, energy,
pressure, and temperature. By "microscopic states", we mean
the exact states of all the molecules making up the system.
Entropy = (Boltzmann's constant k) x logarithm of number of
possible states
= k log(N).

4. Entropy - thermodynamic property-- a
quantitative measure of disorder
Entropy traces out its origin –molecular
movement interpretation-Rudolf Clausias in
1850
The concept of entropy -thermodynamic
laws(i.e. the 2nd law of thermodynamics)
It can be visualised due to the process of
expansion, heating, mixing and reaction.
Entropy is associated with heat and
temperature.

5. Entropy-reflects the degree of disorderness.
Diorderness can be pointed out in three different
types. They are:
Positional disorder
whether the atoms are free to move or not
Vibrational disorder(thermal disorder)
whether the atoms vibrate about an
average position
Configurational disorder
this refers to the distribution of different
atoms or sites in lattice.
Various types of disorder

6. EXAMPLES OF DISORDER

7.  This is one
example of
entropy
 Box 1-less
entropy
 Box 2-more
entropy
Box-1
Box-2

8. Definition and expression of entropy
Entropy may be defined as the property of a system
which measure the degree of disorder or randomness
in the system
 It is a Greek word which means
transformation
 It is denoted by the symbol ‘S’
Clausius was convinced of the significance of the ratio
of heat delivered and the temperature at which it is
delivered,

9. Entropy is the sum total of entropy due to
positional disorder, vibrational disorder and
configurational disorder. i.e randomness due to
change of state
S=sp+st+sc

10. When a system is undergoing change then the entropy
change is equal to the heat absorbed by the system
divided by the temperature at which change taken
place.
ΔS = S2 –S1
= ∫ dq / T
T ΔS = dq or TdS = dq
this is the II law expression.
Suppose the process is undergoing change at constant
temperature:

11. From I Law we know that
ΔE = q – w or dE = dq – dw or dE = dq – PdV
At constant temperature ΔE = 0, therefore dq =
PdV.
From II law we know that dq = TdS ,
Substituting this in the above we get,
Tds = Pdv
ΔS = PdV / T,

12. Suppose the process is undergoing change at constant pressure
condition then:
T ΔS = (q)p -
but we know that (q)p = CpdT
T ΔS = Cp dT,
Or TdS = Cp dT
By integration,
1∫2dS = 1∫2 Cp dT /T
S2 – S1 = Δ Cp ln (T2 / T1)
This is the entropy change of the system at constant pressure condition
from room temperature to the reaction temperature.

13. Importance of entropy in
geochemical thermodynamics
The aim of the thermodynamics in geochemical
term is to generate a set of properties, which helps
us to predict the direction of chemical processes.
The 2nd law starts with simplest term is that there is
an increase in entropy in every natural processes.
The degree of order or disorder in a system may be
described in terms of the probability or
improbability of the observed state,

14.  With the statistical conception of entropy, the possible
application to geochemical systems become recognisable,
 For e.g.- the distribution of energy in geomorphic system is
one way of expressing the relative elevation of particle of
water and sediments etc. in the evolution of landscape.
 It is noted that all natural processes are spontaneous,
unidirectional –where there is increase in randomness.
 Thus this disorderness in the geochemical processes can be
determined by the concept of entropy

15. Applications of entropy
Thermobarometric models
Experimental work in the mineralogy,
petrology etc.
Thermobarometric models are various
thermodynamic formulas or equation by
which pressure temperature are determined,
The model is calibrated through
experimental techniques

16. Thus entropy is applied in the model to
measure the disorderness of the system
through temperature , pressure of the
rock.
Thermobarometry is thus an excellent
case study when the application of
the thermodynamic parameters are
involved

17. Conclusion
Entropy is the thermodynamic property which is
the measure of disorder in a system.
It can be expresses by ‘S’=q/t
The term is coined by Rudolf Clausius.
Entropy is mainly associated with heat and
temperature.
Disorder can be of 3 types- Positional, Vibrational
and Configurational
Thermobarometric models is an excellent case
study when the application of thermodynamic
parameters are involved.

18. It can also be concluded that-
(a) when heat is transferred at a high temperature,
entropy change is small whereas when heat is
transferred at low temperature, entropy change
is greater.
(b) When heat is supplied-entropy increases and
when heat is removed- entropy decreases
Entropy is not perceptible to our sense and there is
no such instrument to measure its effect. Only
changes in entropy can be determined by
computations.
It is usually determined from some specified
arbitrary datum of temperature only.

19. References
 Alok K.Gupta and Sisir K. Sen, a short course on elementary
thermodynamics for earth scientist,96
 Guirlo Ottonello, principles of geochemistry, Columbia University press,
New York, 1893, 151
 Roger Powell, equilibrium thermodynamics in petrology,Hasper and
row publishers, pp 231-232
 W.M White, geochemistry, 2007, pp 44-54
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