Download Unit 2 Thermodynamic parameters Ex.1. Read and learn new words

Unit 2 Thermodynamic parameters
Ex.1. Read and learn new
dam - перемычка
words:
device - устройство
to stipulate –
mercury -ртуть
обусловливать
assume - предполагать
conjugate - сопряженный
to calibrate - градуировать
random - случайный
subtle – трудно
to conserve - сохранять
различимый
angular - угловой
drastic halves - половины
сильнодействующий
scalar - скалярный
negligible незначительный
fraction - частица
to coincide соответствовать
ratio – пропорция
reservoir - резервуар
appreciably - заметный
to alter - изменяться
Ex.2. Read and translate the text:
Thermodynamic parameters
The central concept of thermodynamics is that of energy, the ability to do work. As
stipulated by the first law, the total energy of the system and its surroundings is conserved. It
may be transferred into a body by heating, compression, or addition of matter, and extracted
from a body either by cooling, expansion, or extraction of matter. For comparison, in mechanics,
energy transfer results from a force which causes displacement, the product of the two being the
amount of energy transferred. In a similar way, thermodynamic systems can be thought of as
transferring energy as the result of a generalized force causing a generalized displacement, with
the product of the two being the amount of energy transferred. These thermodynamic forcedisplacement pairs are known as conjugate variables. The most common conjugate
thermodynamic variables are pressure-volume (mechanical parameters), temperature-entropy
(thermal parameters), and chemical potential-particle number (material parameters).
Pressure and Temperature
When we heat an object, we speed up the complex random motion of its molecules. One
method to sidestep the complexity of heat is to ignore heat's atomic nature and concentrate on
quantities like temperature and pressure that tell us about a system's properties as a whole. This
approach is called macroscopic in contrast to the microscopic method of attack. Pressure and
temperature were fairly well understood in the age of Newton and Galileo, hundreds of years
before there were no evidence that atoms and molecules even existed. Unlike the conserved
quantities such as mass, energy, momentum, and angular momentum, neither pressure nor
temperature is additive. Two cups of coffee have twice the heat energy of a single cup, but they
do not have twice the temperature. Likewise, the painful pressure on your eardrums at the bottom
of a pool is not acted if you insert or remove a partition between the two halves of the pool. We
restrict ourselves to a discussion of pressure in uids at rest and in equilibrium. In physics, the
term “uid" is used to mean either a gas or a liquid. The important feature of a uid can be
demonstrated by comparing with a cube of jello on a plate. The jello is a solid. If you shake the
plate from side to side, the jello will respond by shearing, i.e., by slanting its sides, but it will
tend to spring back into its original shape. A solid can sustain shear forces, but a uid cannot. A
uid does not resist a change in shape unless it involves a change in volume.
Pressure
If you're at the bottom of a pool, you can't relieve the pain in your ears by turning your
head. The water's force on your eardrum is always the same, and is always perpendicular to the
surface where the eardrum contacts the water. If your ear is on the east side of your head, the
water's force is to the west. If you keep your ear in the same spot while turning around so your
ear is on the north, the force will still be the same in magnitude, and it will change its direction
so that it is still perpendicular to the eardrum: south. This shows that pressure has no direction in
space, i.e., it is a scalar. The direction of the force is determined by the orientation of the surface
on which the pressure acts, not by the pressure itself. A uid owing over a surface can also exert
frictional forces, which are parallel to the surface, but the present discussion is restricted to uids
at rest. Experiments also show that a uid's force on a surface is proportional to the surface area.
The vast force of the water behind a dam, for example, in proportion to the dam's great surface
area.
Temperature
We use the term temperature casually, but what is it exactly? Roughly speaking,
temperature is a measure of how concentrated the heat energy is in an object. A large, massive
object with very little heat energy in it has a low temperature.
But physics deals with operational denitions, i.e., denitions of how to measure the thing in
question. How do we measure temperature? One common feature of all temperature-measuring
devices is that they must be left for a while in contact with the thing whose temperature is being
measured. When you take your temperature with a fever thermometer, you are waiting for the
mercury inside to come up to the same temperature as your body. The thermometer actually tells
you the temperature of its own working uid (in this case the mercury). In general, the idea of
temperature depends on the concept of thermal equilibrium. When you mix cold eggs from the
refrigerator with our that has been at room temperature, they rapidly reach a compromise
temperature. What determines this compromise temperature is conservation of energy, and the
amount of energy required to heat or cool each substance by one degree.
But without even having constructed a temperature scale, we can see that the important
point is the phenomenon of thermal equilibrium itself: two objects left in contact will approach
the same temperature. We also assume that if object A is at the same temperature as object B,
and B is at the same temperature as C, then A is at the same temperature as C. This statement is
sometimes known as the zeroth law of thermodynamics, so called because after the first, second,
and third laws had been developed, it was realized that there was another law that was even more
fundamental. Thermal expansion the familiar mercury thermometer operates on the principle that
the mercury, its working uid, expands when heated and contracts when cooled. In general, all
substances expand and contract with changes in temperature. The zeroth law of thermodynamics
guarantees that we can construct a comparative scale of temperatures that is independent of what
type of thermometer we use. If a thermometer gives a certain reading when it's in thermal
equilibrium with object A, and also gives the same reading for object B, then A and B must be
the same temperature, regardless of the details of how the thermometers works.
What about constructing a temperature scale in which every degree represents an equal
step in temperature? The Celsius scale has 0 as the freezing point of water and 100 as its boiling
point. The hidden assumption behind all this is that since two points decline a line, any two
thermometers that agree at two points must agree at all other points. In reality if we calibrate a
mercury thermometer and an alcohol thermometer in this way, we will and that a graph of one
thermometer's reading versus the other is not a perfectly straight y = x line. The subtle
inconsistency becomes a drastic one when we try to extend the temperature scale through the
points where mercury and alcohol boil or freeze. Gases, however, are much more consistent
among themselves in their thermal expansion than solids or liquids, and the noble gases like
helium and neon are more consistent with each other than gases in general. Continuing to search
for consistency, we find that noble gases are more consistent with each other when their pressure
is very low.
As an idealization, we imagine a gas in which the atoms interact only with the sides of
the container, not with each other. Such a gas is perfectly nonreactive (as the noble gases very
nearly are), and never condenses to a liquid (as the noble gases do only at extremely low
temperatures). Its atoms take up a negligible fraction of the available volume. Any gas can be
made to behave very much like this if the pressure is extremely low, so that the atoms hardly
ever encounter each other. Such a gas is called an ideal gas, and we decline the Celsius scale in
terms of the volume of the gas in a thermometer whose working substance is an ideal gas
maintained at very low pressure, and which is calibrated at 0 and 100 degrees according to the
melting and boiling points of water. The Celsius scale is not just a comparative scale but an
additive one as well: every step in temperature is equal, and it makes sense to say that the
digerence in temperature between 18 and 28 C is the same as the digerence between 48 and 58 К.
Absolute zero and the kelvin scale the volume becomes zero at nearly the same temperature for
all gases: -273 C. Real gases will all condense into liquids at some temperature above this, but an
ideal gas would achieve zero volume at this temperature, known as absolute zero. The most
useful temperature scale in scientific work is one whose zero is declined by absolute zero, rather
than by some arbitrary standard like the melting point of water. The temperature scale used
universally in scientific work, called the Kelvin scale, is the same as the Celsius scale, but shifted
by 273 degrees to make its zero coincide with absolute zero. Scientists use the Celsius scale only
for comparisons or when a change in temperature is all that is required for a calculation. Only on
the Kelvin scale does it make sense to discuss ratios of temperatures, e.g., to say that one
temperature is twice as hot as another.
Themodynamic instruments
There are two types of thermodynamic instruments, the meter and the reservoir. A
thermodynamic meter is any device which measures any parameter of a thermodynamic system.
In some cases, the thermodynamic parameter is actually defined in terms of an idealized
measuring instrument. For example, the zeroth law states that if two bodies are in thermal
equilibrium with a third body, they are also in thermal equilibrium with each other. This
principle, as noted by James Maxwell in 1872, asserts that it is possible to measure temperature.
An idealized thermometer is a sample of an ideal gas at constant pressure. From the ideal gas
law PV=nRT, the volume of such a sample can be used as an indicator of temperature; in this
manner it defines temperature. Although pressure isdefined mechanically, a pressure-measuring
device, called a barometer may also be constructed from a sample of an ideal gas held at a
constant temperature. Acalorimeter is a device which is used to measure and define the internal
energy of a system.
A thermodynamic reservoir is a system which is so large that it does not appreciably alter
its state parameters when brought into contact with the test system. It is used to impose a
particular value of a state parameter upon the system. For example, a pressure reservoir is a
system at a particular pressure, which imposes that pressure upon any test system that it is
mechanically connected to. The earth's atmosphere is often used as a pressure reservoir.
It is important that these two types of instruments are distinct. A meter does not perform
its task accurately if it behaves like a reservoir of the state variable it is trying to measure. If, for
example, a thermometer were to act as a temperature reservoir it would alter the temperature of
the system being measured, and the reading would be incorrect. Ideal meters have no effect on
the state variables of the system they are measuring.
Ex. 3. Give the Russian equivalents for the following:
conjugate thermodynamic variables, random motion, the conserved quantities, angular
momentum, the term “uid" is used to mean either a gas or a liquid, to spring back, the same in
magnitude, can exert frictional forces, operational denitions, temperature-measuring devices,
all substances expand and contract with changes in temperature, the phenomenon of thermal
equilibrium, mercury thermometer, expands when heated and contracts when cooled, the Celsius
scale has 0 as the freezing point of water and 100 as its boiling point, an alcohol thermometer,
helium and neon, a negligible fraction, according to the melting and boiling points of water,
condense into liquids, coincide with absolute zero, an idealized measuring instrument, a pressure
reservoir.
Ex. 4. Give the English equivalents for the following:
родственные термодинамические переменные, беспорядочное движение, угловое
ускорение, скачок назад, такого же размера, сила трения, приборы для измерения
температуры, тепловое равновесие, ртутный термометр, спиртовой термометр, гелий и
неон, незначительная часть, соответствовать абсолютному нулю.
Ex. 5. Answer the questions:
1. What is the method to sidestep the complexity of heat? Why is it called macroscopic?
2. What is pressure? What experiments show that a uid's force on a surface is proportional
to the surface area?
3. What is temperature?
4. How do we measure temperature?
5. What temperature scale is called the Kelvin scale?
6. What temperature scale is called the Celsius scale?
7. What are thermodynamic instruments?
Ex. 6. Finish the sentences:
1. The most common conjugate thermodynamic variables are…
2. In physics, the term “uid" is used to mean…
The direction of the force is determined by the…
One common feature of all temperature-measuring devices is…
The thermometer actually tells you the temperature…
Thermal expansion the familiar mercury thermometer operates on the principle that the
mercury…
7. The Celsius scale is…
8. The Kelvin scale, is the same as…
9. A thermodynamic reservoir is a system which…
3.
4.
5.
6.
Ex. 7. Speak on:
1. The Celsius scale.
2. The Kelvin scale.
Ex. 8. . Give the English translation of the text:
Heat and Temperature
Thermal energy, or the energy of heat, is really a form of kinetic energy between particles at the
atomic or molecular level: the greater the movement of these particles, the greater the thermal
energy. Heat itself is internal thermal energy that flows from one body of matter to another. It is
not the same as the energy contained in a system—that is, the internal thermal energy of the
system. Rather than being "energy-in-residence," heat is "energy-in-transit."
This may be a little hard to comprehend, but it can be explained in terms of the stone-and-cliff
kinetic energy illustration used above. Just as a system can have no kinetic energy unless
something is moving within it, heat exists only when energy is being transferred. In the above
illustration of mechanical energy, when the stone was sitting on the ground at the top of the cliff,
it was analogous to a particle of internal energy in bodyA. When, at the end, it was again on the
ground—only this time at the bottom of the canyon—it was the same as a particle of internal
energy that has transferred to body B. In between, however, as it was falling from one to the
other, it was equivalent to a unit of heat.
Temperature
In everyday life, people think they know what temperature is: a measure of heat and cold. This is
wrong for two reasons: first, as discussed below, there is no such thing as "cold"—only an
absence of heat. So, then, is temperature a measure of heat? Wrong again.
Imagine two objects, one of mass M and the other with a mass twice as great, or 2 M. Both have
a certain temperature, and the question is, how much heat will be required to raise their
temperature by equal amounts? The answer is that the object of mass 2 M requires twice as much
heat to raise its temperature the same amount. Therefore, temperature cannot possibly be a
measure of heat.
What temperature does indicate is the direction of internal energy flow between bodies, and the
average molecular kinetic energy in transit between those bodies. More simply, though a bit less
precisely, it can be defined as a measure of heat differences. (As for the means by which a
thermometer indicates temperature, that is beyond the parameters of the subject at hand; it is
discussed elsewhere in this volume, in the context of thermal expansion.)
Measuring Heat and Temperature
Temperature, of course, can be measured either by the Fahrenheit or Centigrade scales familiar
in everyday life. Another temperature scale of relevance to the present discussion is the Kelvin
scale, established by William Thomson, Lord Kelvin (1824-1907).
Drawing on the discovery made by French physicist and chemist J. A. C. Charles (1746-1823),
that gas at 0°C (32°F) regularly contracts by about 1/273 of its volume for every Celsius degree
drop in temperature, Thomson derived the value of absolute zero (discussed below)
as −273.15°C (−459.67°F). The Kelvin and Celsius scales are thus directly related: Celsius
temperatures can be converted to Kelvins (for which neither the word nor the symbol for
"degree" are used) by adding 273.15.
Measuring Heat and Heat capacity
Heat, on the other hand, is measured not by degrees (discussed along with the thermometer in the
context of thermal expansion), but by the same units as work. Since energy is the ability to
perform work, heat or work units are also units of energy. The principal unit of energy in the SI
or metric system is the joule (J), equal to 1 newton-meter (N · m), and the primary unit in the
British or English system is the foot-pound (ft ·lb). One foot-pound is equal to 1.356 J, and 1
joule is equal to 0.7376 ft · lb.
Two other units are frequently used for heat as well. In the British system, there is the Btu, or
British thermal unit, equal to 778 ft · lb. or 1,054 J. Btus are often used in reference, for instance,
to the capacity of an air conditioner. An SI unit that is also used in the United States—where
British measures typically still prevail—is the kilocalorie. This is equal to the heat that must be
added to or removed from 1 kilogram of water to change its temperature by 1°C. As its name
suggests, a kilocalorie is 1,000 calories. A calorie is the heat required to change the temperature
in 1 gram of water by 1°C—but the dietary Calorie (capital C), with which most people are
familiar is the same as the kilocalorie.
A kilocalorie is identical to the heat capacity for one kilogram of water. Heat capacity
(sometimes called specific heat capacity or specific heat) is the amount of heat that must be
added to, or removed from, a unit of mass for a given substance to change its temperature by
1°C. This is measured in units of J/kg · °C (joules per kilogram-degree Centigrade), though for
the sake of convenience it is typically rendered in terms of kilojoules (1,000 joules): kJ/kg · °c.
Expressed thus, the specific heat of water 4.185—which is fitting, since a kilocalorie is equal to
4.185 kJ. Water is unique in many aspects, with regard to specific heat, in that it requires far
more heat to raise the temperature of water than that of mercury or iron.
Real – life application
Hot and "Cold"
Earlier, it was stated that there is no such thing as "cold"—a statement hard to believe for
someone who happens to be in Buffalo, New York, or International Falls, Minnesota, during a
February blizzard. Certainly, cold is real as a sensory experience, but in physical terms, cold is
not a "thing"—it is simply the absence of heat.
People will say, for instance, that they put an ice cube in a cup of coffee to cool it, but in terms of
physics, this description is backward: what actually happens is that heat flows from the coffee to
the ice, thus raising its temperature. The resulting temperature is somewhere between that of the
ice cube and the coffee, but one cannot obtain the value simply by averaging the two
temperatures at the beginning of the transfer.
For one thing, the volume of the water in the ice cube is presumably less than that of the water in
the coffee, not to mention the fact that their differing chemical properties may have some minor
effect on the interaction. Most important, however, is the fact that the coffee did not simply
merge with the ice: in transferring heat to the ice cube, the molecules in the coffee expended
some of their internal kinetic energy, losing further heat in the process.
Ex. 9. Make up a project on the following:
1. Hot and "Cold"
Ex. 10.Translate the text into Russian:
Evidence for the kinetic theory
Why does matter have the thermal properties it does? The basic answer must come from the fact
that matter is made of atoms. How, then, do the atoms give rise to the bulk properties we
observe? A crucial observation is that although solids and liquids are nearly incompressible,
gases can be compressed, as when we increase the amount of air in a car's tire while hardly
increasing its volume at all. This makes us suspect that the atoms in a solid are packed shoulder
to shoulder, while a gas is mostly vacuum, with large spaces between molecules. Most liquids
and solids have densities about 1000 times greater than most gases, so evidently each molecule
in a gas is separated from its nearest neighbors by a space something like 10 times the size of the
molecules themselves. If gas molecules have nothing but empty space between them, why don't
the molecules in the room around you just fall to the oor? The only possible answer is that they
are in rapid motion, continually rebounding from the walls, door and ceiling.
The kinetic theory was proposed by Daniel Bernoulli in 1738, and met with considerable
opposition because. There was no precedent for this kind of perpetual motion. No rubber ball,
however elastic, rebounds from a wall with exactly as much energy as it originally had, nor do
we ever observe a collision between balls in which none of the kinetic energy at all is converted
to heat and sound. The analogy is a false one, however. A rubber ball consists of atoms, and
when it is heated in a collision, the heat is a form of motion of those atoms. An individual
molecule, however, cannot possess heat. Likewise sound is a form of bulk motion of molecules,
so colliding molecules in a gas cannot convert their kinetic energy to sound. Molecules can
indeed induce vibrations such as sound waves when they strike the walls of a container, but the
vibrations of the walls are just as likely to impart energy to a gas molecule as to take energy from
it. Indeed, this kind of exchange of energy is the mechanism by which the temperatures of the
gas and its container become equilibrated.
Efficiency and grades of energy
Some forms of energy are more convenient than others in certain situations. You can't run a
spring-powered mechanical clock on a battery, and you can't run a battery-powered clock with
mechanical energy. However, there is no fundamental physical principle that prevents you from
converting 100% of the electrical energy in a battery into mechanical energy or vice-versa. More
ecient motors and generators are being designed every year. In general, the laws of physics
permit perfectly efecient conversion within a broad class of forms of energy. Heat is different.
Friction tends to convert other forms of energy into heat even in the best lubricated machines.
When we slide a book on a table, friction brings it to a stop and converts all its kinetic energy
into heat, but we never observe the opposite process, in which a book spontaneously converts
heat energy into mechanical energy and starts moving! Roughly speaking, heat is different
because it is disorganized. Scrambling an egg is easy. Unscrambling it is harder. We summarize
these observations by saying that heat is a lower grade of energy than other forms such as
mechanical energy. Of course it is possible to convert heat into other forms of energy such as
mechanical energy, and that is what a car engine does with the heat created by exploding the airgasoline mixture. But a car engine is a tremendously inefecient device, and a great deal of the
heat is simply wasted through the radiator and the exhaust. Engineers have never succeeded in
creating a perfectly efecient device for converting heat energy into mechanical energy, and we
now know that this is because of a deeper physical principle that is far more basic than the
design of an engine.
Ex.9. Make up a project on the following:
The Kinetic Theory
Ex. 10. . Give the Russian translation of the text:
Равновесные состояния термодинамических систем могут быть описаны с помощью
небольшого числа макроскопических параметров, таких как температура, давление,
плотность, концентрации компонентов и т. д., которые могут быть измерены
макроскопическими приборами. Описанное таким образом состояние называется
макроскопическим состоянием, и законы термодинамики позволяют установить связь
между макроскопическими параметрами. Если параметр имеет одно и то же значение, не
зависящее от размера любой выделенной части равновесной системы, то он называется
неаддитивным или интенсивным, если же значение параметра пропорционально размеру
части системы, то он называется аддитивным или экстенсивным. Давление и температура
— неаддитивные параметры, а внутренняя энергия и энтропия — аддитивные параметры.
Макроскопические параметры могут подразделяться на внутренние, характеризующие
состояние системы, и внешние, описывающие взаимодействие системы с окружающей
средой и силовыми полями, воздействующими на систему. Так, если газ заключен в сосуд
с подвижными стенками и его объём определяется положением стенок, то объём является
внешним параметром, а давление газа зависит от скоростей теплового движения молекул
и является внутренним параметром. Напротив, если задаётся внешнее давление, то его
можно считать внешним параметром, а объём газа — внутренним параметром.