Document 6517260

Transcription

Document 6517260

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Wisdom
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[email protected] ‫ اﻟﺠﺎﻡﻌﺔ اﻻردﻥﻴﺔ‬,‫ ﻗﺴﻢ اﻟﻬﻨﺪﺳﺔ اﻟﻜﻴﻤﻴﺎﺋﻴﺔ‬,‫ ﻋﻠﻲ ﺧﻠﻒ اﻟﻤﻄﺮ‬.‫د‬
©2003: Ali Al-Matar, Chemical Engineering Dept., University of Jordan
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Lecture 01
Introduction & Basic Concepts
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.
When a wise man does not understand, he
says, 'I do not understand.' The fool and the
uncultured are ashamed of their ignorance.
They remain silent when a question could
bring them wisdom."
Saying of the ABBODS
from The God Makers
by Frank Herbert
[email protected]
Thermo I-Lecture 01: Introduction & Definitions
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What is Thermodynamics?
The Premises:

First Law: Total energy is conserved.
Second Law: Entropy increases.
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A theory is the more impressive the greater the
simplicity of its premises is, the more different kinds
of things it relates, and the more extended is its area
of applicability. Therefore the deep impression which
classical thermodynamics made upon me.
Albert Einstein
Thermodynamics is the study of the changes
in the state or condition of a substance when
changes in its temperature, state of
aggregation, or its internal energy are
important.
Thermodynamics is based upon experimental
observation.
There are five postulates (laws) of
thermodynamics. Two postulates deal with
energy transformation, and the other three
deal with properties.
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1
Thermodynamic Postulates:
Energy Transformation laws
Thermodynamic Postulates:
Property Relationships
First law of thermodynamics. conservation
In a game; you can’t win, even you can’t break
even, and the worst thing is that you have to
keep on playing.
of energy – you can’t get more than what you
invest.
Second law of thermodynamics. It is not
possible to convert all the energy of a system
into useful work – you can eat as much as you
want, eventually, something has to come out.
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each of two systems is in thermal equilibrium
with a third system, they are also in thermal
equilibrium with each other.
Third Law of Thermodynamics- The
entropy of a perfect crystal is zero at absolute
zero temperature.
State Postulate- The state of a simple,
single phase thermodynamic system is
completely specified by two independently
variable, intensive properties.
What is Not Thermodynamics?
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Macroscopic Versus Microscopic
Any (thermodynamic) system can be described
macroscopically or microscopically.
Thermodynamics does not study system dynamics.
That is, it is not concerned with answering: how fast
a system will respond to changes in a constraint or
more?
Thermodynamic considerations do not establish the
rates of chemical or physical processes. Rates
depend on both driving forces and resistances.
Driving forces are thermodynamic variables,
resistances are not.
Thermodynamics is unable to reveal the microscopic
mechanisms of physical or chemical processes.
Zeroth law of thermodynamics- When
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The macroscopic approach considers the system as a
continuum. This results in the system being described
by few variables e.g. pressure, temperature, density
etc. The macroscopic approach is the domain of
classical thermodynamics.
The microscopic approach considers the detailed
molecular nature of the system. This results in the
system being described by a huge number of
variables. We need to specify at least the coordinates
and the momenta of the molecules to describe the
system. The microscopic approach is the domain of
statistical and quantum mechanics.
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2
Many Faceted Science
Statistical Mechanics explains the macroscopic
Classical thermodynamics
properties of matter in terms of its microscopic
details. Thus it enables us to calculate
thermodynamic variables of a system in terms of a
microscopic model of that system. Statistical
mechanics has a predictive power. The tools of
statistical mechanics are general, but the microscopic
models are system-specific.
Thermodynamics provides a description of the
macroscopic properties of matter and their
interrelationships. The laws of thermodynamics
impose inviolable constraints on the behavior of
systems. Thermodynamics is completely general. It
applies to all systems and therein lies its power. Its
results do not depend on the microscopic model of
the system.
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Engineering skills
& vocabulary
Mathematical &
computer skills
Measurable
Measurable(observable)
(observable)quantities
quantities
Temperature,
Temperature,pressure,
pressure,density,
density,heat
heatcapacity,
capacity,composition
composition
Conservation equations
in – out + generation =
accumulation
Conserved quantities
Mass
Moles
Atoms
}
Material balances
Desired products
• Petrochemicals
•
•
•
•
Biochemicals
Advanced materials
Environmental
Nuclear
Energy
Abstract
Abstract(conceptual)
(conceptual)quantities
quantities
Enthalpy,
Enthalpy,entropy,
entropy,chemical
chemicalpotential,
potential,fugacity
fugacity
Result
Result(product,
(product,outcome)
outcome)
Energy
Energyflow
flow
Required
Required
heat
heat
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Road Map to Concepts
Systems of units
(SI, British etc.)
Statistical thermo.
The Road Map to Thermodynamics
Physical
properties
(H, U, Cp, Cv etc.)
Quantum thermo.
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Required
Required
work
work
Equilibrium
Equilibrium
Change
Change
ininstate
state
Chemical
Chemical
equilibria
equilibria
Phase
Phase
equilibria
equilibria
Combined phase
Combined phase
& chemical eqm.
& chemical eqm.
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3
Applications of Thermodynamics
Human
Human body
body
and
and health
health
A system is a three dimensional region of space
DNA
DNA &&
Protein
Protein
folding
folding
Chemical
Chemical
Plants
Plants
Space
Space
System, Surroundings & Universe
Refrigeration
Refrigeration
systems
systems
THERMODYNAMICS
THERMODYNAMICS
Advanced
Advanced
Materials
Materials
Power
Power plants
plants
Automotives
Automotives
Drug
Drug discovery
discovery
Air
Air conditioning
conditioning
Airplanes
Airplanes
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May be real or imaginary
May change size or shape
May be at rest or in motion
The surroundings (or environment) is the region of
physical space outside the arbitrarily selected
boundaries of the system.
The universe is the system and its surroundings.
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Contact Mechanisms

System
Water
Water

Universe = System + Surroundings
Universe
bounded by arbitrary surfaces called walls or
boundaries which delineate the portion of the
universe we are interested in studying.
The walls or boundaries
Surroundings
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The system can be in contact with its
surroundings by three distinct mechanisms:
Mechanical contact. Changes in the pressure
in the surroundings leads to change in the
pressure of the system.
Thermal contact. Changes in the temperature
in the surroundings leads to change in the
temperature of the system.
Material/Chemical contact. The system and
surroundings are able to exchange matter.

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Types of Systems
Thermodynamic Properties
Isolated. Changes in the surroundings do not lead
to changes in the system i.e. there is no mode of
contact between the system and its surroundings.
Closed. Mass is not allowed to be exchanged
between the system and its surroundings.
Adiabatic. The system is prevented from being in
thermal contact with its surroundings.
Open. Mass is allowed to be exchanged between the
system and its surroundings.
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variables called properties which can either
be intensive or extensive.
Any of the intensive variables of the
equilibrium system e.g. T, P, specific volume,
specific energy etc. is a state variable.
The value of any state variable depends only
on the equilibrium state of the system, not on
the path by which the equilibrium state was
reached.
Extrinsic and Intrinsic Properties
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Intensive & Extensive Variables I
Extrinsic properties are quantities whose value
is independent of the nature of the substance
within the system boundaries e.g.,
translational and rotational velocities of a body
around its center
Intrinsic properties are quantities whose value
depend on the nature of the substance
composing the system e.g., density, pressure,
and temperature.

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Properties can be split into two classes
A system is characterized by thermodynamic
Intensive variables are variables that are
independent of the size of the system e.g. T,
P, Density etc. Intensive variables can vary
throughout the system (local distributions,
nonisotropic).
Extensive variables are variables that scale
with the size of the system, and are
proportional to its volume, if other conditions
are kept constant e.g. mass, volume, total
energy etc.
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Intensive & Extensive variables II
Conjugate Variables
Pressure & Volume
Extensive variables can be transformed into
intensive variables by dividing by the total
mass/moles or total volume to obtain
specific properties.
Extensive and intensive variables tend to
come in pairs (conjugate variables). The
incremental work done on a body is the
product of an intensive variable and the
increment in the conjugate extensive
variable.
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Intensive
Kerosene
Water
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Thermodynamic State
Extensive
Generalized force (X) Generalized
displacement (x)
Fluid
Pressure (P)
Volume (V)
Wire (Rubber
band)
Tension (F)
Length (l)
Film
Surface or interfacial Area (A)
tension (γ)
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Generalized
Tension & length
Work = Force × Displacement
System
Interfacial
tension & area
The thermodynamic state of a system is the
condition of the system as characterized by
the values of its properties.
A state property is a property that only
depends on the thermodynamic state of the
system, not the path taken to get to that
state.
Specifying two state variables uniquely
determines the values of all other state
variables of an equilibrium, single-component,
single-phase system.
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Thermodynamic Processes
Reversible Processes I
Reversible processes are these processes
A process is a change or a sequence of
changes in the thermodynamic state of the
system.
The path of the process is the specific series
of states through which the system passes.
A process passing through a succession of
equilibrium states is called quasistatic
process.
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Reversible Processes II
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Iso- Processes
Reversible processes are possible only if
driving forces are infinitesimal, implying that
they are infinitely slow. An idealization which
we approach but we can never attain.
Some factors which render processes
irreversible (natural processes) are friction,
unrestrained expansion of gasses, heat
transfer through a finite temperature
difference, mixing, chemical reaction etc.
which are quasistatic and for which no
dissipative forces are present.
Alternatively: Reversible processes are these
processes in which a second process could be
performed so that the system and
surroundings can be restored to their initial
states with no change in the system or
surroundings.
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Iso means constant
Isothermal process occurs at constant
temperature.
Isobaric process occurs at constant pressure.
Isochoric (isometric) process occurs at
constant volume.

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Cyclic Processes I
Cyclic Processes II
v∫ dy = 0
(1-1)
Conversely, if the integral of a quantity dy
over an arbitrary cycle is zero, then the
quantity y is a property.
system passes through a sequence of states,
ending up back in its original state.
Mathematically the cyclic process can be
represented for any property as
Pressure
A cyclic process is a process such that the
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ti
sta
asi
Qu
c
Rev.
Irrev.
Irrev.
Irrev.
A
D
Volume
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Concept Summary
State Functions versus Path Functions
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Define thermodynamics, and distinguish what is not
thermodynamics.
State functions:
are properties of the system i.e. properties a
substance can possess e.g. T, P, S, U, V, H, A,
and G.
have exact differentials (value depends on
current state)
Path (Process) functions:
are properties of a process i.e. properties only
a process can possess e.g. heat and work.
have inexact differentials (value depends on
how change occurs)
B
C
Differences between classical thermodynamics and statistical
mechanics.
Distinguish what is a measurable and what is an abstract
quantity.
Know problems encountered commonly in thermodynamics.
Define a system, surroundings and universe. Also, know their
contact mechanisms.
Know different kinds of systems and distinguish between them.
Define intensive and extensive variables and their relation with

specific properties.
Define what is a reversible process.
Distinguish between state functions versus path functions.
Know the phase rule and apply it to different situations.
Define what is a phase and know the different phases of matter.
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