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1. SUBJECT:ENTROPYSUBJECT:ENTROPY
NAME:NAME:
PRAJAPATI MAYURPRAJAPATI MAYUR
RATHOD VISHALRATHOD VISHAL
JUNAID SHEIKHJUNAID SHEIKH
ENROLLMENT NO:ENROLLMENT NO:
140950119062140950119062
140950119066140950119066
140950119079140950119079
SEM:3 GUIDED BY :- DEEP SHAH SIRSEM:3 GUIDED BY :- DEEP SHAH SIR
BATCH:MECHB2BATCH:MECHB2
ITM UNIVERSEITM UNIVERSE
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2. Limitations of the First Law of Thermodynamics
∆E = q + w
Euniverse = Esystem + Esurroundings
∆Esystem = -∆Esurroundings
The total energy-mass of the universe is constant.
However, this does not tell us anything about the direction of
change in the universe.
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3. A spontaneous endothermic chemical reaction
water
Ba(OH)2 8H2O(s) + 2NH4NO3(s) Ba2+
(aq) + 2NO3
-
(aq) + 2NH3(aq) + 10H2O(l).
∆H0
rxn = +62.3 kJ
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4. The Concept of Entropy (S)
Entropy refers to the state of order.
A change in order is a change in the number of ways of
arranging the particles, and it is a key factor in determining the
direction of a spontaneous process.
solid liquid gas
more order less order
crystal + liquid ions in solution
more order less order
more order less order
crystal + crystal gases + ions in solution
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5. 1 atm evacuated
Spontaneous expansion of a gas
stopcock
closed
stopcock
opened
0.5 atm 0.5 atm
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6. 1877 Ludwig Boltzman S = k ln W
where S is entropy, W is the number of ways of arranging the
components of a system, and k is a constant (the Boltzman constant),
R/NA (R = universal gas constant, NA = Avogadro’s number.
•A system with relatively few equivalent ways to arrange its
components (smaller W) has relatively less disorder and low entropy.
•A system with many equivalent ways to arrange its components
(larger W) has relatively more disorder and high entropy.
∆Suniverse = ∆Ssystem + ∆Ssurroundings > 0
This is the second law of thermodynamics.
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7. Random motion in a crystal
The third law of
thermodynamics.
A perfect crystal has
zero entropy at a
temperature of
absolute zero.
Ssystem = 0 at 0 K
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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8. Predicting Relative S0
Values of a System
1. Temperature changes
2. Physical states and phase changes
3. Dissolution of a solid or liquid
5. Atomic size or molecular complexity
4. Dissolution of a gas
S0
increases as the temperature rises.
S0
increases as a more ordered phase changes to a less ordered
phase.
S0
of a dissolved solid or liquid is usually greater than the S0
of
the pure solute. However, the extent depends upon the nature of
the solute and solvent.
A gas becomes more ordered when it dissolves in a liquid or
solid.
In similar substances, increases in mass relate directly to entropy.
In allotropic substances, increases in complexity (e.g. bond
flexibility) relate directly to entropy.
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9. NO
NO2
N2O4
Entropy and vibrational motion
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10. Components of ∆S0
universe for spontaneous reactions
exothermic
system becomes more disordered
exothermic
system becomes more ordered
endothermic
system becomes more disordered
∆G0
system = ∆H0
system -
T∆S0
system
∆G0
rxn = Σ m∆G0
products - Σ n∆G0
reactants
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11. Reaction Spontaneity and the Signs of ∆H0
, ∆S0
, and ∆G0
∆H0
∆S0
-T∆S0
∆G0
Description
- + - -
+ - + +
+ + - + or -
- - + + or -
Spontaneous at all T
Nonspontaneous at all T
Spontaneous at higher T;
nonspontaneous at lower T
Spontaneous at lower T;
nonspontaneous at higher T
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12. The effect of temperature on reaction spontaneity
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13. ∆G and the Work a System Can Do
For a spontaneous process, ∆G is the maximum work obtainable from
the system as the process takes place: ∆G = workmax
For a nonspontaneous process, ∆G is the maximum work that must be
done to the system as the process takes place: ∆G = workmax
An example
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14. Free Energy, Equilibrium and Reaction Direction
•If Q/K < 1, then ln Q/K < 0; the reaction proceeds to the right (∆G < 0)
•If Q/K > 1, then ln Q/K > 0; the reaction proceeds to the left (∆G > 0)
•If Q/K = 1, then ln Q/K = 0; the reaction is at equilibrium (∆G = 0)
∆G = RT ln Q/K = RT lnQ - RT lnK
Under standard conditions (1M concentrations, 1atm for gases), Q = 1
and lnQ = 0 so
∆G0
= - RT lnK
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15. FORWARDREACTION
REVERSEREACTION
The Relationship Between ∆G0
and K at 250
C
∆G0
(kJ) K Significance
200
100
50
10
1
0
-1
-10
-50
-100
-200
9x10-36
3x10-18
2x10-9
2x10-2
7x10-1
1
1.5
5x101
6x108
3x1017
1x1035
Essentially no forward reaction;
reverse reaction goes to completion
Forward and reverse reactions
proceed to same extent
Forward reaction goes to
completion; essentially no reverse
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16. The relation between free energy and the extent of reaction
∆G0
< 0
K >1 ∆G0
> 0
K <1
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