Notes on the Text
1. In turn — в свою очередь
TEXT. LIQUIDS
The liquid state occupies an intermediate position between the gaseous and solid states, liquid having a definite volume but no definite shape.
Like a gas, a liquid can take the shape of any vessel in which it is put, but in contrast to a gas, a definite quantity of liquid is required for filling the vessel. A liquid can’t be compressed so much as a gas because its molecules are already close together, large pressure producing small changes in volume.
Increasing in temperature increases the kinetic energy of all molecules.
The change of a liquid into the gaseous or solid states being dependent upon the kinetic energy of the molecules, which in turn is dependent upon the temperature, there are definite temperature characteristics for most liquids at which these changes occur. They are known as transition temperatures.
If we place one liquid layer carefully on top of a layer of a more dense liquid in which it is soluble, and set the vessel where it won’t be disturbed, we shall see that two liquids begin gradually mixing. It is also to be taken into consideration that all liquids do not flow with the same ease, water, alcohol, gasoline flowing easily, while heavy oil, glycerine flowing very slowly.
When a liquid flows, layers of molecules begin rubbing over each other, friction being generated by this rubbing of layers of particles. The greater the friction, the slower is the flow. A liquid which resists flowing, or resists the action of any other deforming force upon it results in a homogeneous solution. We give this example for illustrations that the molecules of a liquid diffuse, though much more slowly than do those of a gas.
The molecules of a liquid are much closer together than they are in a gas, because of the greater relative strength of attraction, the density of liquids being much greater. Naturally as the volume of a liquid begins varying with temperature its density will also start varying with temperature.
It should be noted that the closeness of the molecules also is known as viscous, the opposite of viscosity being fluidity. Viscosity diminishes and fluidity increases with temperature.
Evaporation
The molecules within the interior of a liquid have a definite average energy of motion, and thus a definite mean velocity at each temperature. Some of them, however, at any given instant have a velocity sufficiently greater than the average velocity and this enables them breaking through the surface layer of molecules and escaping. Escaping of molecules from a liquid into its vapour is called evaporation.
Remember
the following words and word combinations:
intermediate
to
disturb
viscosity^
vessel
mean
a
fluidity
^
to
compress
slow(ly)
interior
in
turn . '
gradually
to
enable
<
i
1-J.X
layer
to
rub
surface
carefully
friction
Ex.
10. Answer the following questions:
1. What position does liquid state occupy? 2. What shape does liquid take? 3. Is it possible for a liquid to be compressed? 4. Why is it impossible? 5. What does the change of a liquid into the gaseous or solid states depend on? 6. What will happen if we place one liquid layer on top of a layer of a more dense liquid in which it is soluble? 7. Do all liquids flow with the same ease? 8. What is the friction generated by?
Why are the molecules of a liquid much closer together than those of a gas? 10. What is evaporation?
Ex. 11. Translate the following sentences into Russian paying attention to the meanings of the words in bold type:
1. The temperature of the sun is intensely high. 2. This substance is highly insoluble in water. 3. The increase of . energy stored in the gas, because of the rise in temperature, is called the increase of internal energy. 4. Solids that conduct heat readily are called good conductors. 5. This reaction should be watched closely because it is very important for the final results. 6. If you close this container, the reaction will stop. 7. A solid body has a definite shape, its molecules acting as though they were closely bound to one another.
It is very important to remember that melting occurs without any change in temperature. 9. Any change in temperature influences the pressure. 10. The closer we bring two charged bodies together the more attraction or repulsion they will exercise on each other.
Ex. 12. Remember the following synonyms:
because of — due to to differ—to vary
to change—to alter mean—average
to occur—to take place force—strength
for example — for instance
Ex. 13. Find the pairs of antonyms and remember them:
rapidly, liquid, definite, decrease, solid, indefinite, increase, ease, heavy, difficulty, light, slowly.
Ex. 14. Translate the following sentences, mind the “ing”-forms:
1. After melting, the average speed of the molecules remains the same as before but the molecules are now free of each other. 2. The process of overcoming the attractive forces between the molecules of a substance is called melting. 3. The only difference between waves transmitting heat radiation and radio waves is the difference in the wave length. 4. Instead of increasing the temperature of the ice, the energy is used in decreasing the attraction between the ice molecules. 5. The temperature of the melted ice rising, the movement of its molecules is speeded up. 6. In the process of boiling heat is constantly added to the liquid. 7. When a liquid boils evaporation takes place throughout the volume of the liquid, small bubbles of vapour forming within the liquid. 8. By increasing the pressure, however, the substance can be obtained in a liquid state, provided the change from liquid to solid is accompanied by an expansion. 9. As we have seen, adding heat to a substance will not always cause a rise of its temperature. 10. It is only the fast moving molecules that are able to escape from a liquid surface. 11. When a liquid starts boiling at a certain temperature and under a given pressure, the heat causes the liquid to vaporize.
Every liquid can have a definite vapour pressure, this pressure increasing with rising temperature. 13. The vapour pressure of a liquid becoming equal to atmospheric pressure, the liquid boils. 14. They succeeded in getting good results after a number of tedious investigations. 15. The steam expanding its volume will increase. 16. This resulted in increasing the temperature greatly. 17. The rate of evaporation also depends on evaporating surface. 18. Since gases expand on heating and contract on cooling, it is interesting to consider, what will happen if v/e continue lowering their temperature. 19. A thermometer bulb exposed to direct sunlight becomes much hotter than the surrounding air. 20. Using a thermometer, it is possible to transform power at low voltage into power at high voltage, power at high voltage being also transformed into power at low voltage.
Ex. 15. Translate the following sentences into Russian, mind the words in bold type:
1. Having absorbed much heat, the aluminium when it is cooled can give up the same quantity of heat. 2. The energy lost by the hot water is equal to the energy transferred to the cold water. 3. The wire being very thin and the current being large, the amount of generated heat is greater than that in the thick wire. 4. The wire, being very thin, was very good for our experiment. 5. The melting point of pure iron is about 1,535°C, most steels melting at about 1,300 to l,5Q0°C. 6. A gas being heated at constant pressure, work is done by the gas when it expands. 7. The problem having been solved, we could go home.
The vapour pressure of a solid at any temperature being greater than one atmosphere, the substance will pass directly from the solid to the vaporous condition. 9. A solid body having been melted, the change of state took place at a definite temperature. 10. Experiments using a constant source of heat show that heat must be supplied to melt the solid. 11. The quantity of heat required for the changing the unit mass of a substance from the solid to the liquid state without any change of temperature is called the latent heat. 12. The liquid, being lighter than mercury, rises. 13. The silicon atom, being only slightly heavier than the aluminium atom and a bit smaller in radius, is also very active. 14. Having four electrons in its outer level with light electrons in the next lower level, the atom may attain stability by either losing four electrons or gaining four electrons. 15. The process of electrification is, therefore, not one of creating electricity but of transferring electrons from one material to another. 16. In passing through the metal electrons must collide with many ions. 17. In making up a condenser, one has to take into consideration its size, as the amount of charge that a condenser stores depends on its size.
Ex. 16. Read the text and retell it:
When equilibrium exists between any liquid and its;ya- pour, the number of molecules contained in a unit volume of vapour is constant, and hence the pressure exerted by a vapour at equilibrium is constant.
The pressure exerted by a vapour in equilibrium with its liquid is known as the vapour pressure of that liquid. The greater the number of gas molecules in a specific space and the greater their average speed, the greater will be the pressure they exert. Vapour pressure is to be determined experimentally.
A rather simple method consists of setting up a barometer tube and noting the height of the mercury. Then a small quantity of the liquid which is to be tested is put at the bottom of this tube.
The liquid, being lighter than mercury, rises to the top of the mercury column, where it evaporates into the empty space of the closed tube. The pressure of the vapour above the mercury column causes it to be depressed. Then if we subtract the height of the column from the original height, we shall obtain the vapour pressure.
Ex. 17. Translate the text using a dictionary. Analyse the “ing”-forms:
A liquid being cooled, its molecules lose energy. The cooling process being conducted slowly, the particles which constitute the solid may arrange themselves into definite positions. The solid itself will exist in a regular geometric form called a crystal. Crystals are of various forms and of varying degrees of strength and rigidity, both these properties depending upon the substance of which they are composed.
Having learned this, we can state that the properties of matter in the gaseous state are determined largely by the motion of particles, while in the solid state they are determined largely by the rigidity of the structure formed and by the position which the particles occupy with respect to each other in the structure, these latter being dependent upon the magnitude of the forces of attraction and upon the size of the particles.
Ex. 18. Read the text and render it:
The molecules within the interior of a liquid have a definite average energy of motion, and thus a definite average velocity at each temperature. Some of them, however, at any given instant, have a velocity sufficiently greater than the average velocity to enable them to break through the surface layer of molecules and escape. Thereafter they are
free to wander about in the space above (see Fig. 6) and constitute a vapour — namely a gas that can be condensed to a liquid merely by increasing the pressure upon it. (Air is not a vapour, for to condense it to a liquid it must be both compressed and cooled.)
The
escape of molecules from a liquid into its vapour is called
evaporation. A liquid that evaporates readily is volatile. After a
sufficient number of molecules have collected in the space above
the liquid, their haphazard wanderings bring them back to the surface
as Fig.
6. fast
as other molecules escape. Thereafter, there is a balance between
evaporation and recondensation and thus a constant number of
molecules within the closed space at any given moment; and these, by
bombardment of the walls of the vessel set up a constant pressure,
called the vapour pressure.
Ex. 19. Describe the following experiment (use Fig. 7):
If some iodine crystals are put into a flask, which is then stoppered and allowed to stand at room temperature, it will