chemical equilibrium and thermodynamics

chem.Eql

1. E Eduncie]

se à given process including a chemical
under a given

For example, thermodynamics predicts that hydrogen and oxygen gases would react at ordina
temperature to yield quid water. Bu it does not toll whether the reaction wil be fast or slow. We know

Only from experiment that in the absence of a catalyst, the reaction is extremely slow.

The study of thermodynamics is based on treo generalization derived from experimental results
ion are known as first, second and third law of thermodynamics based on human
ere is no formal proo for them,

THERMODYNAMICS TERMINOLOGY
¡grs aro mainly used in thermodynamics are given below
System : A system is defined as a specified potion of matter parated from the
rest ofthe universe with a bounding surface
Surrounding : The rest of universe which can interact withthe system, is surroundings
Isolated System : A system which can exchange neither energy nor mater with is
surrounding is called isolated
Closed System : A

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2. E Eduncie]

‘Adiabatic Process : À process is termed as adiabatic if no exchang takes place
between the system and surroundings,
For adiabatic process; dQ = 0

Isobaric Process : A proc med as iscbarc if pressure ofthe system remain
constant during each step o the process.

For isobaric process; dp = 0

Isochorie Process : The process termed as isochori if volume of the system remains
‘constant Le, dv = 0
Cyclic Process : The process is termed as cycle, when a system undergoes a number
of dite os and finaly returns to ts intial state, fo 0, and
dH =

REVERSIBLE AND IRREVERSIBLE PROCESS

(0 Reversible Process : A process which oocurs infiitesimaly slowly o that diving force

is only infinitesimally greater than the opposing force is called a reversible process.
A reversible process cannot be realised in practico because it would require infinito time for

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3. EE Edunci

This isthe mathematical statements ofthe fist aw of thermodynamics, In this statement, Q is
heat absorbed and W is the work done on the system

In caso Q is the heat absorbed and w the work Im, then the relationship becomes
AU Om

I work ig done on the system, W is taken as positive so Ihat AU = Q + W if, however work is

ystem, W is taken as negative so that AU = Q W
Enthalpy (4)
1. Heat change at Constant Pressure

according to frs
Q-ae+W “
at constant pressure the work of expansion (WW) may be replaced by PAV, where AV is the
change in volume.

So equation (1) taken the form

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4. EE Edunci

or BE-C-aT

= Heat capaci at Constant P

Heat Capacity at Constan

The difference between C, and ©, is equal to work done by 1 mole of gas in expansion w
heated through 1"
Werk done by gas at con
for 1 mole of gas PV = RT
hen temperature is rai lume become +

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5. E Eduncie]

internal energy fora given substance in a given state is impossible, But one thing is certain that the
internal energy of a parieuar system is a definte quantiy at the given moment, respective of the
manner by which i has been obtained. Internal energy ike temperature, pressure, volame, et. is a stale
function, Le, total of all possible kinds of energy of a system is called its Internal energy’.

His neither possible nor necessary to calculate the absolute vale of internal energy of a system.
In thermodynamics, one is concerned only with energy change which occurs when the system moves
from one state to another. Let AE be the diference of energy ofthe intial state (E) and the final state
(then
ESE-E
AE is positive i E, > E, and negative i E, < E
System may ransler energy to or from the suroundings as heat or work or both

Characteristics of Internal Energy

© Internal energy of a sive prope

(Internal energy is a state property.

(i) The change in the internal energy does not depend on the path by which the fina sta

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6. Edunci 1

The work done by the gas in an infinitesimal expansion is thus given by
aw = - Pav
‘The total work w done by the gas in expansion of ideal gas from volume

w--[pav

nat

P

CRUE
Integrating,

W--nRTig,

to volume V, i

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7. HE Eduncie]

rk done during intermediate isothermal expansi

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8. HE Eduncie]

G INT/T) = = Rin
o TT) = (RC) VV,
Gace A

INT = (7-1) INV VA = Ing
1/7, (Y
Te

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9. Edunci 1

TR-TR,
PP,

A
WC, TT)

TP TP,

[
W=C,(T, -T)=-Rp. | TRE

Thus knowing G, T,, P,, P, and P.,, we can ready calculate T,, the final temperature ofthe
Reversible Isothermal Expansion of Real Gas
We shall not deve expres {or the reversible isothermal expansion of
real gas.
(A) Work of expansion
{he work done in the expansion is given
Pav

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10. HE Eduncie]

Irtegratino,
feu-u

(©) Heat Change
from the fist law of thermody

aU Qs w
o Q=au-w
‘Substituting the value for W and AU

(Q-nRT i
(0) Enthalpy Change (AH)
We know that

Heu

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11. HE Eduncie]

se RT]
Vo

Comparison of Work of Expan Gas. We kno
an ideal gas, numerically
Wu = ART In (V e

and lora 3, rom work of expansion numerical

1
28). a

V2 nb, then Eq.10 reduces:
Wan = DAT e

Hence, numerically

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12. Edunci 1

energy. Consegueni the Internal energy of he 5
PU + PV, = U = U,
o UPN
o H-H
Thus, the Jo e 9 x ergy but
th constant enthalpy. Ths 5
Joule-Thomson Coefficient

I u, has positive value, the gas cools on expansion.
y, has negative warms on expansion
for ag. H, He et.

aol Un, has N eee is observed,

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13. HE Eduncie]

The Eq. - 4 may be written as

ET
>

Pv)
5) ‚(sw
for an ideal ga

7

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14. HE Eduncie]

9.14, may be

SH) _ 2a

e), AT

4) and Ea (16) we have

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15. HE Eduncie]

Fig. : Exothermic reactions
Endothermic Reactions
Such reactions + accompanied by absorption of heat, are called endothermic reaction
for endothermic reaction:
AH = Positive
for positive value of aH

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16. HE Eduncie]

(0): AH = -97.6 Keal/mot
Ena à mot
Thus, enthalpy of formation of HCI is -22 Kcal mot

Enthalpy of Combustion
The amount of heal evolved when one mole of substance is Completely ox

Loc example

890.3k

285,29K Jmol
Enthalpy of Solution

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17. Edunci 1

based on thermochemical changes taking place in the formation of a atico. This
cycle can be used to determine ‘gy which cannot bo drocly measured. Ii defined as that
released when one moe of the ionic compound (late) is formed its isolated ions inthe gaseours
state under standard condi
nA~(g) + mB(Q) > AB,
AH = -U (lattice energ
Formation of NACI) latico involves thus

1e 200 Eye

U can be calculated
enthalpy of sublimation on Ne
1 ionisaton of energy of Na) = Al
2 = bond energy
U = lation energy

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18. EE Edunci

Applications of Hess's Law
1. Caleulation of Enthalpies of Reactions :

Hess law makes it Possible to calculate enthalpies of many reactions which cannot be determined
experimental

Carbondioxde is the same, viz, 393.5 kJ, whether the reaction takes place in à single step as

8) + 0,(9) —>00.(9) aH = 3995 kd

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19. HE Eduncie]

CRETE » 34,000)

Adéing (w) and (v) and substracting (D, we get
» CH aH = 49.0 ks
ne is + 49 kd
KIRCHHOFF's EQUATION
fariaton of heat of the reaction with temperature is expressed mathomat
Is known ask ktchhoft's equation,
;chhott's Equation at Constant Pressure

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20. HE Eduncie]

the value of bond energies of

O-H bond

Application of Bond Energy
1. Heat of Reaction

Heat of reaction

foe example

CH, CH)
Cand H-H are 9

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21. E Eduncie]

pH, RE - RE,
CALORIMETRY-MEASURING HEATS OF REACTIONS

Al calorimeti techniques are

based on the measurement of heat that may be
(exothermic process), consumed (endothermic process) or simply dissipated by

humerous methods to measure such heat Any pr

amp
wth the environment is

ass that resuts in heat being generated and exchan
Jorimeto study
eve used to me

ure heat of 1
reactions, we often en

1, In order

alorimeter inate the reaction, and measure the temperature
ditference before and aer the reaction, The temperature difference enables us to evaluate the heat
released inthe reaction

Two basic types of cal are discussed

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22. Oxygen supply

nition

megnitying
eyepiece

N
ignition cot! — Sample steel bomb
imeter measures the heat evolved under constant
here AT isthe temperature increase. The a, so measured is also called the change in inter
energy AE.
AE = q, ar
Mustration
1. Acalorimetor with heat capacity equivalent to having 13.3 moles of water is used to measure th
heat of combustion from 0.303 a D,). The temperature increase was found
be 5.0 K. Calcular 1 released by 1.0 9, and 1.0 me

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23. Edunci 1

\ )
dou carats am
The heat capaciy ofthe calorimeter can also be determined by burning an exactly known
of a standard substance, whose enthalpy of combustion has been determined. Ben:
is one such standard, The problem below ilustrates the calculato
Hustraion
3. When0.1025 g of benzoic acid was burnt in a bomb calorimeter {ho temperature
increased by 2.165" C. For benzoic acid AH

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24. E Eduncie]

Carnot completed a cycle consisting of four reversible operations such that after the fourth
‘operation the system reverts back unchanged tos nda starting poston, The operations ae (1) revers
isothermal expansion, (I reversible adiabatic expansion, Il) reversible isothermal compression, and (IV

reversible adiabatic compres

The temperatures in (I) and ll) are T, and T, respectively and T, > T, because after the second
operation the temperature must fall. The parameters at diferent points are shown in the
car diagram (Fig). The adiabatic cues are steeper because during these operations PV = constant,

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25. EE Edunci

ZA, Tin VW
The effeleney x, of the engine is gi

W_AG,- Tiny,
ATAN

The efficiency of a Carnot engine thus depends only on the temperature ofthe source and the
sink, and not on any other factor example, say the nature o, o the amount ofthe working substance.

Since, (T,-T.) < T, herelore the elicieny is always less than unit, Le. an engine operating in
cycles cannot convert heat completely into work. Only if T, = 0 K, then and then only n = 1 and
consequently W = Q.. So complete conversion of heat into work can be elected only if the sink can be

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26. EE Edunci

entropy
+ Envopy is denoted by 's
‘© Entopy stands for wo greek work
En - identity with energy
tope - Change
+ Entopy is measure of randomness or disordemess of a molecular sys

‘© is ifieu to deine the actual entropy of a system

Itis more convenient to define the change of entropy during a change of state.

Thus change of entropy of a system may be define as the summation of all the terms each
involving heat exchange (a), divided by the absolute temperature (T) during each infinitesimally small
change of the pro

Thus entropy change fora finite change of state of a system at Constant temperature is given by

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27. HE Eduncie]

Spontaneity in Term of Entropy Change
A thermodynam i accompanied by an ino
surrounding taken together while in a thermodynamical re
stem and its surounding taken together remains unalere

we may put the above statement in the form ing mathematical expressions:
(8S, + 8S) = 0 (For reversible
XS, + AS) > 0 (For ireversible P

Combining the two, we get

ESS 0

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28. Edunci 1

BT
Trouton’s Law : For many liquids, the entropy of on atthe normal boling Point has.
approximately the same value
90 sik mot
So, AH 90 Jc! mot! x T,
+ Trouions law falle for associated liquid vater, alcohol
‘© also fail for substrate with boling point of 150 k or below.
Entropy Change in Cyclic Reversible Process
In a Complete oye the total entropy Change of a system must be zero, since it has retuned
its Original thermodynamic stato

hence

Entropy Change of an Ideal Gas

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29. HE Eduncie]

moles ofthe ideal gast
Rin

his evident thatthe entropy change forthe change of sate
inal and final volumes as well as on the inital and final temperatur
(li) When T and P are the Two Variables
IP, is the Pressure of the ideal gas in th intial state and P,
Py, = AT,
V, = ATP.
PY, » RT,

jaion may be writen as

an ideal gas depends upon the

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30. HE Eduncie]

1crease in temperature of an ide accompanied by increase in
entropy
(8) Isochor
in ime remain constant
HT]
Evidently, increase in temperature ol an ideal gas ta constant volume is accompanied by increase
in entropy.
l process, the entropy. Remains constant and hence As should be zero
then fom equation

Em TIT, = AMPTP, RN, TP

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31. HE Eduncie]

E, (Gin T = RP +
REninx
LR nan à nn + a)
RENTE
ri and x represent Ihe number of moles and the mole fraction 1
the total entropy of mixing
Free Energy
Free Energy Change and Spontaneity
In the fee energy change of a chemical re can take place

spontaneously Ifthe free energy chan fate of equitxium and the free

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32. EE Edunci

1. Exothermic Process
In the Case of exothermic reaction
Le (Favorable Condition)
Cases : When TAS is «Ve (lavorable), nen AG wäl be negative and the process vil be spontaneot
at all temperature

Case : When TAS is -Ve (unfaverable), then AG wil be negative when AH > TAS, To reduce

the magnitude of TAS, the temperature should be lo

Thus, exothermic reactions can bo made favourable (When TAS = -Ve) by lowering the temperature
2. Endothermic Process
In the case of endothermic proce
AH = «Ve (unfavorable Condition)

gnitude of TAS,

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33. EE Edunci

equal tothe reversible
Gibbs Free Energy
he function that is Particularly applicable to Constant pressure i called Gibbs free ener

itis denoted by <
His given by
GeH-Ts
But HE + PV
G-E+P
G-a+P
AwE-TS
AG = AA + AU
AG = AA + PAY + VAP.
hen pressure is constant then

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34. HE Eduncie]

hange ol free energy when a system undergoes reversibly process, a
change ol temperature

0, then ea. (6)

case - 11
1 temperature is constant
GT =0, thon equation (6)

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35. EE Edunci

these relationship gives the variation ofthe work function with temperature & volume,
Maxwell Relationship

The various expr Connecting intemal energy (U),enthalpy (+), Helmhote free ener
and Gibbs free energy (G), With relevant Parameters such as entropy, Pressure, temperature and
lume may be put as

D dU=Tds - Pav

dhe TOS + oP

n (yields the result

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36. HE Eduncie]

For inital state
Ser,
For final state

We also know that

OT + Vip

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37. EE Edunci

is called the forward reaction and the oppose
on is called rever
For example

(1) CH,COOH + NaOH = CHE

(2) FeCl, + 3,0 = Fe(OH)

Po,

State of Chemical Equilibrium
Chemical equiibrium in a re

jereible reaction is ne sta

‘rection Le, forward reaction ony is called

¡reversible reaction
For example
H + HOL> NaCl + H,O +

) Mn, 2K!
6) Bac! (a0) + H,SO, (ac) =>

BaSO/()L + 2H01 (aa)

at which both fon

reactions or two opposing reaction occur at the same speed,

RE

no

c+0

Rate of forward reaction

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65) + 30,

19

38. HE Eduncie]

Rate of forward reaction (R,) « [AÏ [BP or k (A (8)

KI = Rate Constant for forward reaction
{ON or Kb (CF [D
K, = Rate Constant for backward ro

Rate of back ward reaction (A) « (C

A equilibrium
(Ar Br

where k, I called oquiibrium Constant
‘centration (active mass) of Pure solid and pure liquid are

on of Ke

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39. HE Eduncie]

or
then ke far

ke

s gi
PER;
ke BE

Potting the value of PP and RE trom t

out)

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40. HE Eduncie]

eauibrium ©

> Dis given a

Effect of Temperature on K
According to Arthenious equation

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41. HE Eduncie]

reactions, increase in temperature increases the k value

)ve, i, heat is release

ase temperature, decreases the equilibrium constant K.

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42. EE Edunci

These eletraytes are almo pletely
ised in apolar solvent and they

behaves as poor Conductors of electric

for exam for examples - CH,COOH, HPO, HBO,
NaOH, etc NHOH ato

Arrhenius Theory of Electrolytic Dissociation
(1) Postulates of Arrhenius Theory
® In aqueous solution, the molecules of an electrolyte undergo spontaneous dissociatios
form positive and negative ions
Degree of ionization (a)

No.of dissocited molecules

Tolal no of molecules of elecrolye before dissociation

At moderate Concentration, there exist an equiibrium between the on and undissociated

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43. HE Eduncie]

2 of K, depends upon
Nature of electoy
Natur of solvent
Temperature,
lution, the temperature i ied, the K, valve will depend
on the nature of el
foe very

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44. EE Edunci

ine 48-84 ‘Sea water

P of Mixture

ample - 2
Pras
(HI = 10m
10% x 1+10

(Hore MR = Resultant molariy)

Butter Solution
‘There are some solution which have definte pH Le, their pH do not change by the add

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45. EE Edunci

(CH,COOH is suppressed by adétion of an acid due to Common ion eff

+ on addition of Base -»
+ OH > CH,COO + HO
10 OH ions furnished by a base are removed and P o the solution is Practically unal
Basic Butter Solution
Weak base + salt of (W.B + SA)
For exampl NHLOH + NHC

NHOH — NH, + OH
NH Cl — NH + ct

Ho
Case : On adtion of acid

NHLOH + H- — NH,

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46. HE Eduncie]

and when fa

For Basic Butter

[POH = pk

knowing pOH, pH can be calculated by the application ofthe formula
[roo]

Butter Capacity
His the number of moles of H: ion or OH ion that should be added to 1 lire ofa buffer solution

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47. HE Eduncie]

be regarded as constants

[HAJIBOH) no
‘pay ““HOI-K
led hydrolysis.

(i Degree of Hydrolysis: I is defined as the fa percentage) ofthe total sat which is
4 at equilrium for example I 90% of a "y 5 degree of

No.of moles of the salt hycrolysec

= Total numberof moles of sal taken

Type of salt Exp for Kh Exp for h

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48. HE Eduncie]

Solubility Product
In a saturated solution of an

AB — AB

sold unionised
Applying the law of mas

the electrolyte is
y at a paricular tempora
ie, {AB} = K = Constant

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49. HE Eduncie]

(1) Elecrayte of ype AB,

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50. Edunci 1

In general

inal cone 10%
Calculation of Simultaneous Solubility
Solubility o two electrolytes having Common ion; when they are dissolved in the same solution,
imultaneous solubility

ally strong (having close solubility produc
When sob 2, Le, they one not equal)

CaF, (ky = 34
Application of solubility product +
(Purification of Common salt +

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51. HE Eduncie]

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