2013 lecture 1 introduction to thermodynamics
TRANSCRIPT
CY1001 BASIC CONCEPTS
T. Pradeep 22574208
9/19/2013 1
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
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
Joseph Black, 1728 - 1799 Francis Bacon 1561-1626