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Thermodynamics
This lecture note includes information derived from various internet sources.
What is it?
Thermodynamics is the study of heat and its effects on matter. Thermodynamics follows four basic laws.
Give me an example!
It is important to understand thermodynamics because heat often changes the chemical and physical
properties of things. For example, the air inside the same automobile tire on a cold day takes up less space
than that same air in that same tire on a hot day.
Matter
What is it?
Matter is the substance that everything is made of. Matter can exist in a gas, liquid, or solid state. Matter
can be a pure element or any type of compound.
All Matter has three basic characteristics: First, matter has volume (takes up space). Second, matter has
mass (or can be weighed). And third, matter has inertia.
Give me an example!
Water is matter which is all around us in many forms. We drink it as a liquid. We use it to cool things in its
solid state (ice). And we use it for heat when it's a gas (steam). It's all the same matter - just in different
states.
Inertia
What is it?
In physics, inertia is the force of nature that makes matter tend to maintain or stay in its current state of
motion. Inertia is the resistance of objects to any change in their speed. Every object has inertia, and the
amount of inertia an object has is directly related to the amount of mass it has; the more mass, the more
inertia, and therefore the more resistance to change in speed.
In chemistry, inert substances are those which will not react with others. There is a group of elements in the
periodic_table_of_the_elements called the "Noble Gasses" which are chemically inert. You can find them on
the right side of the periodic table in the very last column, under helium (He).
Give me an example!
Have you ever pulled a toy wagon? Did you notice that the more things you put into the wagon - the more
mass it contained - the harder it was to pull? That's because the more mass the wagon contained, the more
inertia acted upon it.
First Law of Thermodynamics
What is it?
The First Law of Thermodynamics states that the amount of heat energy contained within a closed system
is always constant. This is the basis of the principle of conservation_of_energy.
Give me an example!
When a battery powered light is switched on and heat is produced, that heat energy actually already existed
inside the system as chemical energy inside the battery. So no energy is either gained or lost as a result of
switching on the light.
Conservation of Energy
What is it?
Conservation of energy is a physical_law which states that energy can be converted to a different form, but
it is never lost all together.
Give me an example!
When the internal_combustion_engine in an automobile burns gasoline, it produces heat energy. The engine
then uses this heat to drive pistons and turn a crankshaft, converting the heat to mechanical energy. The
heat energy is not lost - merely changed to another kind of energy.
Zeroth Law of Thermodynamics
What is it?
The Zeroth Law of Thermodynamics states that if two systems both achieve thermodynamic_equilibrium
with a third system, then the two systems will also be in equilibrium with each other, too.
Give me an example!
If you set a pan of boiling water and a tray of ice cubes out in the same room for several hours, the
temperature of the boiling water will decrease to the temperature of the room - and the ice will melt and
therefore increa
Thermodynamic Equilibrium
What is it?
Thermodynamic equilibrium is when heat ceases to flow between two systems. There is no heat_transfer
when thermodynamic equilibrium is reached.
Give me an example!
If you put a hot cup of coffee or tea in a cold room, heat will flow from the cup and its contents into the room.
But if you leave it there for two hours and come back, the cup of coffee or tea will be at the same
temperature as the room. The coffee and the room will have achieved a state of thermodynamic
equilibrium.
Second Law of Thermodynamics
What is it?
The Second Law of Thermodynamics states that it is impossible to completely convert heat energy into
mechanical energy. Another way to put that is to say that the level of entropy (or tendency toward
randomness) in a closed system is always either constant or increasing.
Give me an example!
Have you ever felt the heat from exhaust coming out of the tailpipe of a car? Automobile engines are
designed to convert the heat energy resulting from the combustion of gasoline into mechanical energy.
However, this process does not function with 100% efficiency - and proof of that is the heat lost along with
the exhaust gasses.
Entropy
What is it?
Entropy is the scientific measurement of the change in the randomness or disorder in a chemical system as
the result of a reaction. A positive change in entropy means the system is less ordered after the reaction
than it was before.
Give me an example!
Have you ever watched an ice cube melt at room temperature? You were watching entropy in action! As the
ice passes from a solid state to a liquid state, the level of entropy (or randomness) of the molecules rises.
Third Law of Thermodynamics
What is it?
The Third Law of Thermodynamics states that the entropy of all crystaline solids approaches zero as their
temperature approches absolute_zero. In other words, all substances lose their energy at absolute zero.
Give me an example!
Have you ever wondered why people keep food in a deep freeze? Lowering the temperature of the food
preserves keeps the food from losing energy and decomposing. That way when you want to eat a frozen
pizza, you take it out of the freezer, add heat, and you have a hot, mouthwatering meal!
Solid
What is it?
Solid is one of the three states or phases_of_matter.
A solid substance does not flow (like a liquid does) and does not take on the shape of the container in which
it is being kept (again, like liquids do). If a solid is heated, it will become a liquid once it reaches its
melting_point.
Give me an example!
Have you ever frozen water to make ice? Then you have turned a liquid into a solid. If you melt ice, you are
turning a solid into a liquid.
Absolute Zero
What is it?
Absolute zero is the temperature at which no known system can still engage in heat_transfer. Absolute
zero is the temperature where all molecular motion ceases.
On a Kelvin thermometer, absolute zero is simply "zero." On a Celsius thermometer, absolute zero is at 273 degrees. Absolute zero is the lowest temperature in the world, and has never actually been attained in
a laboratory.
Give me an example!
When you freeze water into ice, the molecules form a solid crystalline structure and move much less than
when the water is in its liquid phase. If you continue to lower the temperature of the ice, you will reach a point
where all molecular motion comes to a standstill - theoretically, at absolute zero.
Temperature
What is it?
Temperature is a measurement of the amount of heat a substance contains. There are three major
temperature scales: Fahrenheit, Celsius, and Kelvin.
Give me an example!
Have you ever had your temperature taken with a thermometer? The thermometer contains a liquid that is
heated by your body and expands inside a tube. Measured markings on the sides of the tube tell how hot
you are, which is how the doctor tells whether you have a fever - by taking your temperature.
Kelvin
What is it?
The Kelvin temperature scale is often used in scientific experiments. Zero degrees Kelvin is called absolute
zero because it is the temperature where every element in the periodic_table_of_the_elements will freeze.
Water will freeze at 273 degrees Kelvin. Water reaches its boiling_point at 373 degrees Kelvin.
Give me an example!
Converting a Kelvin reading to Celsius is easy - just add 273 to the Kelvin reading. Want to convert a
Kelvin temperature to Fahrenheit? First add 273 to the Kelvin reading, and then convert it as if it were a
Celsius reading - multiply by 9/5 and add 32.
thermodynamics
thermodynamics (thûr´mo-dì-nàm´îks), branch of science concerned with the nature of HEAT and its
conversion into other forms of energy. Heat is a form of energy associated with the positions and motion of
the molecules of a body. The total energy that a body contains as a result of the positions and the motions of
its molecules is called its internal energy. The first law of thermodynamics states that in any process the
change in a system's internal energy is equal to the heat absorbed from the environment minus the WORK
done on the environment. This law is a general form of the law of conservation of energy (see
CONSERVATION LAWS). The second law of thermodynamics states that in a system the entropy cannot
decrease for any spontaneous process. A consequence of this law is that an engine can deliver work only
when heat is transferred from a hot reservoir to a cold reservoir or heat sink. The third law of
thermodynamics states that all bodies at absolute zero would have the same entropy; this state is defined as
having zero entropy.
entropy
entropy, quantity specifying the amount of disorder or randomness in a system bearing energy or
information. In thermodynamics, entropy indicates the degree to which a given quantity of thermal energy is
available for doing useful work-the greater the entropy, the less available the energy. According to the
second law of thermodynamics, during any process the change in entropy of a system and its surroundings
is either zero or positive; thus the entropy of the universe as a whole tends towards a maximum. In
information theory entropy represents the "noise," or random errors, occurring in the transmission of signals
or messages.
energy
energy, in physics, the ability or capacity to do work. Forms of energy include heat, chemical energy, and,
according to the theory of relativity, mass; other forms of energy are associated with the transmission of light,
sound, and electricity. When a force acts on a body, the work performed (and the energy expended) is the
product of the force and the distance over which it is exerted.
Potential energy is the capacity for doing work that a
body possesses because of its position or condition.
For example, a weight lifted to a certain height has
potential energy because of its position in earth's
gravitational field. Kinetic energy, the energy a body
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posesses because it is in motion, is equal to ½mv ,
where m is its mass and v is its velocity. The average
kinetic energy of the atoms or molecules of a body is
measured by the temperature of the body. Energy (or
its equivalent in mass) can be neither created nor
destroyed, but it can be changed from one form into
another.
motion
motion, in mechanics, the change in position of one body with respect to another. The study of the motion of
bodies is called dynamics. The time rate of linear motion in a given direction by a body is its velocity; this rate
is called the speed if the direction is unspecified. If during a time t a body travels over a distance s, then the
average speed of that body is s/t. The change in velocity (in magnitude and/or direction) of a body with
respect to time is its acceleration. The relationship between force and motion was expressed by Isaac
Newton's three laws of motion:
A body at rest tends to remain at rest, or a body in motion tends to remain in motion at a constant speed in a
straight line, unless acted on by an outside force;
The acceleration a of a mass m by a force F is directly proportional to the force and inversely proportional to
the mass, or a = F/m;
For every action there is an equal and opposite reaction. The third law implies that the total linear momentum
(mass m times velocity v) of a system of bodies not acted on by an external force remains constant (see
conservation laws).
Motion at speeds approaching that of light must be described by Einstein's special theory of relativity, and
the motions of extremely small objects (atoms and elementary particles) are described by quantum
mechanics.
mechanics
mechanics (mî-kàn'îks), branch of physics concerned with motion and the forces causing it. The field
includes the study of the mechanical properties of matter, such as DENSITY, elasticity (see STRENGTH OF
MATERIALS), and VISCOSITY. Mechanics is divided into STATICS, which deals with bodies at rest or in
equilibrium, and dynamics, which deals with bodies in motion. Isaac Newton, who derived three laws of
motion and the law of universal gravitation, was the founder of modern mechanics. For bodies moving at
speeds close to that of light, Newtonian mechanics is superseded by the theory of relativity, and for the study
of very small objects, such as elementary particles, quantum mechanics is used.
conservation laws
conservation laws, in physics, basic laws that maintain that the total value of certain quantities remains
unchanged during a physical process. Conserved quantities include mass (or matter), energy, linear
momentum, angular momentum, and electric charge; the theory of relativity, however, combines the laws of
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conservation of mass and of energy into a single law (E=mc ). Additional conservation laws have meaning
only on the subatomic level.
Special Theory of Relativity
relativity (rèl´e-tîv¹î-tê), physical theory, introduced by Albert Einstein, that discards the concept of absolute
motion and instead treats only relative motion between two systems or frames of reference. Space and time
are no longer viewed as separate, independent entities but rather as forming a four-dimensional continuum
called space-time. In 1905 Einstein enunciated the special theory of relativity, in which the hypothesis that
the laws of nature are the same in different moving systems also applies to the propagation of light, so that
the measured speed of light is constant for all observers regardless of the motion of the observer or of the
source of light. From these hypotheses Einstein reformulated the mathematical equations of physics. In most
phenomena of ordinary experience the results from the special theory approximate those based on
Newtonian dynamics, but the results deviate greatly for phenomena occurring at velocities approaching the
speed of light. Among the assertions and consequences of the special theory are the propositions:
the maximum velocity attainable in the universe is that of light (c)
mass increases with velocity
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mass and energy are equivalent (E=mc )
objects appear to contract in the direction of motion (Lorentz contraction)
the rate of a moving clock seems to decrease as its velocity increases (time dilation)
events that appear simultaneous to an observer in one system may not appear simultaneous to an observer
in another system.
The special theory became the foundation of the study of elementary particles and of quantum mechanics.
elementary particles
elementary particles, the most basic physical constituents of the universe. Atoms are the basic units of the
chemical elements but are themselves composed of smaller particles. The first subatomic particle to be
discovered was the electron, identified in 1897 by Joseph John Thomson. The nucleus of ordinary hydrogen
was subsequently recognized as a single particle and was named the proton. The third basic particle in an
atom, the neutron, was discovered in 1932. Although models of the atom consisting of just these three
particles are sufficient to account for all forms of chemical behavior of matter, quantum mechanics predicted
the existence of additional elementary particles.
Decades of painstaking experiments and theoretical
insights have led to a surprisingly simple picture of
the world of elementary particles and the laws they
obey. According to this physical theory, known as the
Standard Model, the most fundamental particles fall
into three categories: the leptons, the quarks, and the
gauge bosons (force carriers). Leptons include the
electrically charged electrons, two unstable particles
similar, but heavier than electrons, and neutral
particles called neutrinos.
Two kinds of quarks, called "up" and "down", make up the protons and neutrons, but heavier, less stable
quarks also exist. Gauge bosons give rise to the strong, weak, and electromagnetic forces, which govern the
interaction of the quarks and leptons. A more detailed chart summarizes the properties of the particles in the
standard model.
quantum mechanics or quantum theory
quantum mechanics or quantum theory, branch of mathematical physics that deals with the emission and
absorption of energy by matter and with the motion of material particles. Because it holds that energy and
matter exist in tiny, discrete amounts, quantum mechanics is particularly applicable to elementary particles
and the interactions between them. According to the older theories of classical physics, energy is treated
solely as a continuous phenomenon (i.e., waves), and matter is assumed to occupy a very specific region of
space and to move in a continuous manner. According to the quantum theory, energy is emitted and
absorbed in a small packet, called a quantum (pl. quanta), which in some situations behaves as particles of
matter do; particles exhibit certain wavelike properties when in motion and are no longer viewed as localized
in a given region but as spread out to some degree. The quantum theory thus proposes a dual nature for
both waves and particles, with one aspect predominating in some situations and the other predominating in
other situations.
Quantum mechanics is needed to explain many properties of matter, such as the temperature dependence
of the specific heat of solids, as well as when very small quantities of matter or energy are involved, as in the
interaction of elementary particles and fields, but the theory of relativity assumes importance in the special
situation where very large speeds are involved. Together they form the theoretical basis of modern physics.
(The results of classical physics approximate those of quantum mechanics for large scale events and those
of relativity when ordinary speeds are involved.)
Quantum theory was developed principally over a period of thirty years. The first contribution was the
explanation of blackbody radiation in 1900 by Max Planck, who proposed that the energies of any harmonic
oscillator, such as the atoms of a blackbody radiator, are restricted to certain values, each of which is an
integral (whole number) multiple of a basic minimum value. In 1905 Albert Einstein proposed that the
radiation itself is also quantized, and he used the new theory to explain the Photoelectric Effect. Niels Bohr
used the quantum theory in 1913 to explain both atomic structure and atomic spectra, showing the
connection between the energy levels of an atom's electrons and the frequencies of light given off and
absorbed by the atom. Quantum mechanics, the final mathematical formulation of the quantum theory, was
developed during the 1920s. In 1924 Louis de Broglie proposed that particles exhibit wavelike properties.
This hypothesis was confirmed experimentally in 1927 by Clinton J. Davisson and Lester H. Germer, who
observed diffraction of a beam of electrons. Two different formulations of quantum mechanics were
presented following de Broglie's suggestion. The wave mechanics of Erwin Schrödinger (1926) involves the
use of a mathematical entity, the wave function, which is related to the probability of finding a particle at a
given point in space. The matrix mechanics of Werner Heisenberg (1925) makes no mention of wave
functions or similar concepts but was shown to be mathematically equivalent to Schrödinger's theory.
Quantum mechanics was combined with the theory of relativity in the formulation of P.A.M. Dirac (1928),
which also predicted the existence of antiparticles. A particularly important discovery of the quantum theory
is the uncertainty principle, enunciated by Heisenberg in 1927, which places an absolute theoretical limit on
the accuracy of certain measurements; as a result, the assumption by earlier scientists that the physical state
of a system could be measured exactly and used to predict future states had to be abandoned. Other
developments of the theory include quantum statistics, presented in one form by Einstein and S.N. Bose
(Bose-Einstein statistics, which apply to bosons) and in another by Dirac and Enrico FERMI (Fermi-Dirac
statistics, which apply to fermions); quantum electronics, which deals with interactions involving quantum
energy levels and resonance, as in lasers; quantum gravitation, the quantum theory of gravitational fields;
and quantum field theory. In quantum field theory, interactions between particles result from the exchange of
quanta: electromagnetic forces arise from the exchange of photons, weak nuclear forces from the exchange
of W and Z particles, strong nuclear forces from the exchange of gluons, and gravitation from the exchange
of gravitons.
atom
atom, the smallest unit of a chemical element having the properties of that element. An atom contains
several kinds of particles. Its central core, the nucleus, consists of positively charged particles, called
protons, and uncharged particles, called neutrons held together by the strong force. Surrounding the nucleus
and orbiting it are negatively charged particles, called electrons. Each atom has an equal number of protons
and electrons unless it has been ionized. The nucleus occupies only a tiny fraction of an atom's volume but
contains almost all of its mass. Electrons in the outermost orbits determine the atom's chemical and electrical
properties. The number of protons in an atom's nucleus is called the atomic number and determines which
element it is. The number of nucleons (protons and neutrons in the nucleus) is the atom's mass number.
Atoms containing the same number of protons but different numbers of neutrons are isotopes of the element.
The atomic weight is the average mass of an atom of an element in atomic mass units. One atomic mass
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unit (1 AMU=1.6606x10 kg) is 1/12th the mass of the C isotope. The atomic weight may involve an
average over several naturally occuring isotopes of the element. The mass of atoms other than hydrogen is
different from the sum of the masses of the neutrons and protons in the nucleus because of the binding
energy of the nucleus. See also history of the atom, standard units.
History of the atom
History of the atom: In the 5th cent. B.C. the Greek philosophers Democritus and Leucippus proposed that
matter was made up of tiny, indivisible particles in constant motion. Aristotle, however, did not accept the
theory, and it was ignored for centuries. Modern atomic theory began with the publication in 1808 by John
Dalton of his experimental conclusions that all atoms of an element have same size and weight, and that
atoms of elements unite chemically in simple numerical ratios (as molecules) to form compounds. In 1911
Ernest Rutherford explained an atom's structure in terms of a positively charged nucleus surrounded by
negatively charged electrons orbiting around it. In 1913 Niels Bohr used quantum theory to explain why
electrons could remain in certain allowed orbits without radiating energy. The development of quantum
mechanics during the 1920s resulted in a satisfactory explanation of all phenomena related to the role of
electrons in atoms.