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8/12/2019 Cap 1 Termodinmica q
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Captulo 1
Termodinmica Qumica
Professor Osvaldo Chiavone Filho
DEQ/UFRN
2013.2
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THE SCOPE OF
THERMODYNAMICS
The science of thermodynamics was born in the nineteenth
century of the need to describe the operation of steam engines
and to set forth the limits of what they can accomplish. Thus the
name itself denotes power developed from heat, with obviousapplication to heat engines, of which the steam engine was the
initial example. However, the principlesobserved to be valid for
engines are readily generalized, and are known as the first and
second laws of thermodynamics. These laws have no proof in themathematical sense; their validity lies in the absence of contrary
experience. Thus thermodynamics shares with mechanics and
electromagnetism a basis in primitive laws.
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THE SCOPE OF
THERMODYNAMICS
These laws lead through mathematical deduction to a network of
equationswhich find application in all branches of science and
engineering. The chemical engineer copes with a particularlywide
variety of problems. Among them are calculation of heat and workrequirements for physical and chemical processes, and the
determination of equilibrium conditions for chemical reactions and
for the transfer of chemical species between phases.
Thermodynamic considerations do not establish the rates of chemicalor physical processes. Rates depend on driving force and resistance.
Although driving forces are thermodynamic variables, resistances are
not. Neither can thermodynamics, a macroscopic-property
formulation, reveal the microscopic (molecular) mechanisms of
physical or chemical processes.
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THE SCOPE OF THERMODYNAMICSOn the other hand, knowledge of the microscopic behavior of matter
can be useful in the calculation of thermodynamic properties.Property values are essential to the practical application of
thermodynamics. The chemical engineer deals with many chemical
species, and experimental data are often lacking. This has led to
development of "generalized correlations that provide propertyestimates in the absence of data.
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TYPES OF THERMODYNAMICS
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The application of thermodynamics to any real problem starts with
the identification of a particular body of matter as the focus ofattention. This body of matter is called the system, and its
thermodynamic state is defined by a few measurable macroscopic
properties. These depend on the fundamental dimensions of science,
of which length, time, mass, temperature, and amount of substanceare of interest here.
APPLICATION OF THERMODYNAMICS
P = presso
T = temperatura
x= composio
= densidade
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Projeto de Processos
(Ex. Extrao por Solvente)
1
2
3
4
5
67
8
9
10
11
12
13
14
15
W1
11
T1
W2
T2
12
32
W3T
3
13
23
W7
T7
W6
T6
W4
T4
Vd
Ae
W5
T5W
8T8
W9
T9
W10
T10
W11
T11
W12
T12
Ac
Ar
W13
T13
W14
T14
W15
T15
14
24
extrato
rafinado produto
guagua
vapor
EVAPORADOREXTRATOR
CONDENSADORRESFRIADOR
MISTURADOR
alimentao
bomba
decantador
solvente
condensado
f
f
f
f f
f
f
f
x11
x14
31
Dimensionamento
Simulao
Otimizao ($)
Anlise de Sensibilidade
W = vazo
T = temperaturaV = volume
A = rea
x= composio
fij= fluxo comp. i
e corrente j
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Avano do Equilbrio Lquido-
Vapor por Conta da Destilao
0.00 0.20 0.40 0.60 0.80 1.00
Frao molar de pentano
300.0
350.0
400.0
450.0
500.0
Temper
atura(K)
Lquido
Vapor
L + V
Experimental
Acima pto Crtico
UNIQUAC
Destilao - Gs de Cozinha T-xy C5+C12 a 100 kPa
Planta Qumica Tpica (50% do $)
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DIMENSIONS AND UNITS
The fundamental dimensions are primitives, recognized through
our sensory perceptions and not definable in terms of anything
simpler. Their use, however, requires the definition of arbitrary
scales of measure, divided into specific units of size. Primary unitshave been set by international agreement, and are codified as the
International System of Units (abbreviated SI, for Systme
International).
Time: s (Cesium cycle)
Length: m
Mass: kg
Mole: symbol mol, is defined as the amount of substance
represented by molecules.
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PREFIXES FOR SI UNITS
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TEMPERATURE, K
Termmetro a Gs Ideal
P v = R T
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Force, N
Exerccio:Um astronauta pesa 730 N em Houston, Texas, onde a aceleraoda gravidade g= 9,792 m s-2. Quais so a massa e o seu peso nalua, onde g= 1,67 m s-2?
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Pressure, Pa
Manmetro a contrapeso
A
mg
A
FP
Ahm
ghA
gAhP
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Pressure, PaQual a presso Pdo tanque com ar indicado pela figura a seguir em
Pa, sabendo que a presso atmosfrica igual 750 mmHg e que omanmetro de mercrio registra uma quota de 35 cm.
760 mmHg = 101325 Pa
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Work, Pa
Diagrama P-V
dlFdW
A
VdAPdW
dVPdW
2
1
V
VdVPW
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Kinetic EnergyWhen a body of mass m, acted upon by a force F, is displaced a
distance dl during a differential interval of time dt, the work done is
given by F dl.In combination with Newton's second law:
dlamdW dldt
dumdW duumdW
22
2
1
2
22
1
mumuduumdW
u
u
2
2
1muEK
Potential EnergyIf a body of mass mis raised from an initial elevation z1to a final
elevation z1, an upward force at least equal to the weight of the bodymust be exerted on it, and this force must move through the distance
z2-z1. Since the weight of the body is the force of gravity on it, the
minimum force required is given by Newton's law:
gmamF
)()( 1212 zzgmzzFW gzmEP
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Energy ConservationIn any examination of physical processes, an attempt is made to find
or to define quantities which remain constant regardless of the
changes which occur. One such quantity, early recognized in thedevelopment of mechanics, is mass. The great utility of the law of
conservation of mass suggests that further conservation principles
could be of comparable value. Thus the development of the concept
of energy logically led to the principle of its conservation inmechanical processes. If a body is given energy when it is elevated,
then the body conserves or retains this energy until it performs the
work of which it is capable. An elevated body, allowed to fall freely,
gains in kinetic energy what it loses in potential energy so that its
capacity for doing work remains unchanged. For a freely falling body
this means that:
0 PK EE 0
22
12
2
1
2
2 gmzgmzmumu
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HeatWe know from experience that a hot object brought in contact with a
cold object becomes cooler, whereas the cold object becomes
warmer. A reasonable view is that something is transferred from thehot object to the cold one, and we call that something heat Q. Thus
we say that heat always flows from a higher temperature to a lower
one. This leads to the concept of temperature as the driving force for
the transfer of energy as heat. More precisely, the rate of heattransfer from one body to another is proportional to the temperature
difference between the two bodies; when there is no temperature
difference, there is no net transfer of heat. In the thermodynamic
sense, heat is never regarded as being stored within a body. Like
work, it exists only as energy in transit from one body to another, or
between a system and its surroundings. When energy in the form of
heat is added to a body, it is stored not as heat but as kinetic and
potential energy of the atoms and molecules making up the body.
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HeatIn spite of the transient nature of heat, it is often viewed in relation to
its effect on the body from which it is transferred. As a matter of fact,
until about 1930, the definitions of units of heat were based on thetemperature changes of a unit mass of water. Thus the British thermal
unit (commonly known as thermochemical Btu) was long defined as
1/180thquantity of heat which when transferred to one pound mass
of water raised its temperature from ice-point or 32 (F) to steam-point or 212 (F) at standard atmospheric pressure.. Likewise the
calorie (commonly known as thermochemical calorie) written as (cal)
in the book, was defined as 1/100thquantity of heat which when
transferred to one kilogram mass of water raised its temperature
from 0 to 100C (273.15 to 373.15 K) at standard atmospheric
pressure. Although these definitions provide a "feel" for the size of
heat units, they depend on experiments made with water and are
thus subject to change as measurements become more accurate.
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HeatIn order to recognize a common basis for all energy units,
international steam table calorie is defined in relation to joule, the SI
unit of energy, equal to 1 N m. Joule is the mechanical work donewhen a force of one newton acts through a distance of one meter. By
definition, international steam table calorie is equivalent to 4.1868 J
(exact) and thermochemical calorie is equivalent to 4.184 J (exact). By
arithmetic, using the defined relations of US Customary and SI units,one international steam table Btu, written as (Btu) in the book, is
equivalent to 1055.056 J as against one thermochemical Btu is
equivalent to 1054.35 J. All other energy units are defined as
multiples of the joule. The foot-pound force, for example, is
equivalent to 1.355 8 179 J while the meter-kilogram force is
equivalent to 9.806 65 J. The SI unit of power is the watt, symbol W,
defined as energy rate of one joule per second.