CY1001 BASIC CONCEPTS

T. Pradeep 22574208

pradeep@iitm.ac.in

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Lecture 1

Atomists and ionists

1. Chemical thermodynamics 2. Statistical thermodynamics 3. Kinetics 4. Surface science Books: 1. Kuhn Hans, Försterling Horst-Dieter and Waldeck David H, Priniples of Physical Chemistry, 2nd Ed., Wiley(2009). 2. Atkins P W and de Paula Julio, Physical Chemistry, Oxford University Press, 8th Ed., (Indian Student Edition) (2009). 3. Silbey Robert J, Alberty Robert A, Bawendi Moungi G., Physical Chemistry, (4th Ed.), Wiley (2006). Lecture schedule Tutorials Evaluation

Property

Variable Time

Quantum mechanics Statistical mechanics Thermodynamics

Variation of heat with process

UNIVERSE

4

SYSTEM SURROUNDING

OPEN CLOSED ISOLATED

Pressure, Volume, Temperature, Heat, Mass

Intensive and Extensive Variables

What is unique about Thermodynamics?

Independent of atomic and molecular theory. In chemical systems, thermodynamics helps to keep a record of energy flow. Equilibrium state of a chemical system can be understood from thermodynamics. It is a logical science, three statements describe thermodynamics; deductions from these laws constitute the equations. Validity of thermodynamic laws depends only on the basic laws and the logical deductions which follow from them. Since thermodynamics is itself a science, not dependent upon the foundations of other branches, it has an existence of its own.

A theory is the more impressive the greater the simplicity of its premises, the more different kinds of things it relates, and the more extended its area of applicability. Hence the deep impression that classical thermodynamics made upon me. It is the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown. Albert Einstein

System

Surroundings

Characterization of a system Based on properties

(1) intensive properties and (2) extensive properties

Types of systems (1) open, (2) closed, and (3) isolated systems.

(1) homogeneous or (2) heterogeneous

Chemical system Phase, Component

Process, Path

State function, Path function Exact and inexact differentials

Zeroth Law A B and B C, then A C { = thermal equilibrium}

First Law Law of conservation of energy

Work, heat Exothermic, endothermic

First Law

dU = dq – dw Internal energy of an isolated system is constant

Work = -PexdV

Free expansion = 0 Isothermal work = ∫ -(nRT/V) dV = - nRT ln Vf/Vi

(reversible)

PexdV

Pex

Vi Vf

P

Indicator diagram James Watt

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q and w are positive, when energy is transferred to the system q and w are negative, when energy is lost from the system Exact and Inexact differentials

∫ −≠=∂b

aab wwww )(

Exact differential

Inexact differential

UUUdUb

aab ∆=−=∫

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Sum of two inexact differentials can be an exact differential (first law)

Test for exactness-Euler's theorem ),( yxfz = dy

yzdx

xzdz

xy

∂∂

+

∂∂

=if then,

When yxxy y

zxx

zy

∂∂

∂∂

=

∂∂

∂∂

Then z is an

exact differential

Inexact differentials can be converted to exact differentials by multiplying with integrating factors

The General Expression for Work

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From Physics, Work, w = Fd cos θ

When θ = 1800, Work, w = -Fd dw = -F.dz But, F = Pressure x Area = P.A

Therefore, dw = -P.A.dz

Now, A.dz = dV

dw = -P.dV

F

w

∫−=2

1

V

V

PdVw

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Concept of reversibility

P1, V1, T

m

m h P1

P2

V2 V1 P1, V1 P2, V2

SINGLE STEP COMPRESSION

)( 122 VVPmghw −−==

Two, three and infinite number of steps

Same compression can be Done with less work !

∫ ∫−=∂=2

1

V

V

PdVww

AmgP =2

Different situations

• Free expansion • Expansion against constant pressure

If P is constant,

• Isothermal reversible expansion

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F w

w = - P (V2 – V1)

∫−=2

1

V

V VdVnRTw

1

2lnVVnRTw −=

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dVVUdT

TUdU

TV

∂∂

+

∂∂

=

HEAT CAPACITY U as a function of T and V

dVVUPdT

TUq

Text

V

∂∂

++

∂∂

=∂

dVPqdU ext−∂=Since,

At constant volume,

dTUq

V

V

∂∂

=∂

VV

V CTU

dTq

=

∂∂

=∂ Heat capacity at constant volume

CdTq

=∂ Path dependant

(constant V or T)

HEAT CAPACITY

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∫=∆2

1

T

TVV dTCU

VV T

UC

∂∂

=

If CV is constant over a small range of temperature, TCU VV ∆=∆

gas vacuum

We have seen that, dVVUdT

TUdU

TV

∂∂

+

∂∂

=

0=

∂∂

= dVVUdU

T Since Joule Found that q∂ = 0;

and w∂ =0 0=

∂∂

TVU

Since dV≠0,

This is not correct for real gases.

Internal Pressure

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H = U + PV

Change of state at constant pressure Enthalpy

)12(12 VVPqpVPqUUU P −−=∆−=−=∆

( ) ( )1122 PVUPVUqP +−+=

12 HHqP −=

dHqP =∂

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dPPHdT

THdH

TP

∂∂

+

∂∂

=H as a function of T and P

and at constant P, dHqP =∂Since

Heat capacity at constant pressure

If CP is independent of temperature, TCH P∆=∆

dTTHq

P

P

∂∂

=∂

PP

P CTH

dTq

=

∂∂

=∂

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CP - CV = nR dV

VUPdT

TUq

Text

V

P

∂∂

++

∂∂

=∂

divide by dT and setting PP C

dTdq

=

PTVP T

VVUPCC

∂∂

∂∂

+=−

For an ideal gas, and PnR

TV

P

=

∂∂

0=

∂∂

TVU

nRCC VP =−∴

Enthalpy, H = U + PV Calorimetry

Isotherm and adiabat

Thermochemistry Heat of formation, ΔfHo

Hess’s Law

Born-Haber Cycle

Kirchhoff’s equation

ΔrHo (T2) = ΔrHo (T1) + ʃ ΔrCp

o

Equipartition principle

Ad Isotherm P α1/V Adiabat

P α1/Vγ

P

V

dT

Joule experiment ΠT = (∂U/ ∂V)T Joule-Thomson Experiment μ = (∂T/ ∂P)H

Just to know

Galileo Galilei 1564-1642

It is all about heat…. Thermodynam

ics, History

Joseph Black, 1728 - 1799 Francis Bacon 1561-1626

James Prescott Joule 1818-1889

James Watt 1736 - 1819

Sadi Carnot 1796-1832

Rudolf Clausius 1822 - 1888

Lord Kelvin (William Thomson) 1824-1907

Ludwig Boltzmann 1844-1906

Josiah Willard Gibbs 1839-1903

Jacobus Henricus van 't Hoff 1852-1911

Walther Hermann Nernst 1864 - 1941

Gilbert Newton Lewis 1875-1946