ContentsIntroductionImportance of concept of entropy in geochemical thermodynamicsVarious types of disorderDefinition and Expression of

entropyApplication of entropy ConclusionReferences

Monday 1 May 2023

Introduction 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.

Various types of disorderEntropy-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.

EXAMPLES OF DISORDER

This is one example of entropy

Box 1-less entropy

Box 2-more entropy

Box-1 Box-2

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,

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

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:

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,

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.

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,

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

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

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

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.

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.

ReferencesAlok K.Gupta and Sisir K. Sen, a short course on elementary thermodynamics for earth scientist,96

Brain Mason and Carleton B Moore, principles of geochemistry, fourth edition, Wiley eastern limited, PP 65-68

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

44-54www.google.com

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