Solids and gases represent the extreme states of behaviour of molcculcs. The liquid state can be thought of as an intermediate condition in which some of the properties found in cither solids or gases arc displayed. Liquids, like gases arc isotropic and flow readily under applied stress, but like solids, they arc dense, relatively incompressible, and have properties that arc largely determined by the nature and strength of intcrmolecular forces. With respect to molecular order, liquids arc substances considered to be intermediate between solids and gases. The fact that liquids arc isotropic tells us immediately that they do not have the extended latticc structure and long-range order of solids. Yet, the density of a liquid is generally only 10% less than that of its solid phase; this must mean that the molecules in a liquid are packcd together with some regularity, and do not exhibit the complete chaos associated with molcculcs in the gas phase.
One of the most important properties of liquids is their ability of acting as solvents. In the first place, liquid solutions provide an extremely convenient means of bringing together carcfully measured amounts of reagents and of allowing them to react in a controlled manner. Second, the nature of the reactions which proceed and the speed at which they occur can be greatly influenced by the properties of the liquid solvent medium. Finally, the physical properties of solutions arc interesting and important, because they can be used to determine molecular weights of dissolved substances and to study the nature and strength of forccs between solvent and solute molcculcs.
One of the most engaging and absorbing features of the study of chcmistry is the attempt to explain the behaviour of bulk matter in terms of molecular properties. Therefore, it is important to outline a molecular picture which will help us to understand and relate phenomena associated with the liquid state.
Words and Word-Combinations to Be Memorized
ability, absorb, bulk, complete, convenient, display, engage, generally, intermediate, intcrmolecular, lattice, a means, outline, reagent, range, with respect to, solute, strength
Ex. 5. Give the Russian equivalents for the following:
I think of, display some properties, dense, intcrmolccular forces, with respect to, immediately, the latticc structure, the long-range order, mean, be packed together, provide a means of, carcfully measured, procccd, findlly, bccausc, the behaviour of bulk matter, outline a picturc, be associated with, the strength of forces
Ex. 6. Give the English equivalents for the following:
поведение молекул, жидкое состояние, либо... либо..., главным образом, порядок расположения молекул, занимать промежуточное положение между, на 10% меньше (больше), плотность жидкости, способность действовать в качестве растворителя, протекать с определенной скоростью, оказывать большое влияние, физичсские свойства растворов, определить атомный вес, растворенное вещество, растворитель, растворимое вещество
Ex. 7. Fill in the blanks with articles where nccessary.
1.... liquid state can be thought of as intermediate condition between ... solids and gases. 2. ... properties of liquids are determined by ... nature and strength of... intcrmolccular forces. 3 density of... liquid is
generally only 10% less than that of... solid. 4. Their ability of acting as ... solvents is one of... most important properties of... liquids. 5. It is important to outline ... molecular picturc of... liquid state.
Ex. 8. Give synonyms for the following:
think of, display, under stress, largely, immediately, little, allow, influence, feature, explain
Ex. 9. Give antonyms for the following:
incompressible, extend, long-range, less, convenient, be influenced by, most important
Ex. 10. Translate the sentences into Russian.
1. One should follow the proceeding reaction very carcfully. 2. Selenium, an clement belonging to the sulphur group, is as much non- metal as metal. 3. Many factors mentioned determine the reaction rate. 4. There is a striking resemblance between some elements. 5. St. Petersburg University has its own publishing house. 6. The boiling point of water is accepted to be 100°C. 7. Some objections were found to the Arrhcnius theory long believed to be true. 8. The most striking thing about hydrogen is its extreme lightness. 9. An acid is defined as a compound or an ion capable of liberating a proton. 10. Two or more atoms having identical nuclear chaigcs but different numbers of Acutrons are said to be isotopes. 11. Ores containing as little as 2 per ccnt or even less of coppcr or nickcl arc worth mining. 12. Bond formation involving
elements toward the middle of the periodic table occurs by the proccss of electron sharing. 13. There are a number of different procedures being used in qualitative analysis. 14. The calculation of hydrogen ion concentration in a solution containing a weak electrolyte is a difficult one for the average student first facing this problem. IS. Sulphur dioxide is more than twice as heavy as air and is one of the most easily liquefied gases known. 16. The term "heat** of combustion refers to the amount of heat liberated per mole of the substancc burned. 17. Many industrial processes depend for their success upon the solubilities of the compounds formed. 18. The system of chcmical symbols now used was proposed by the Swedish chcmist Bcrzelius in 1818. 19. Fluorine, though for a long time known to exist, was not isolated until 1886. 20. There has been, sincc earliest times, an atomic hypothesis thought to be implied by the diffusion and the compressibility of gases on the one hand and by the symmetry of crystalline solids on the other. 21. The question of the composition of air long supposed to be one of the elements was solved only in the 18th ccntury. 22. Dangerous bacteria in drinking water may be killed by small amounts of chlorinc. 23. An clement is represented by ccrtain letters for case in writing. This symbol stands for one atom of the clement. 24. There are numerous methods for demonstrating the spectra of many of the elements. 25. In qualitative analysis there is usually greater difficulty in diagnosing the cations present than in recognizing the anions. 26. In English, wc have the practicc of naming chcmical elements in Greek and Latin. 27. As a rule, there are several ways of preparing an element. 28. Mercury has the property, unusual for a metal, of being a liquid at room temperature. 29. The phenomena likely to arise during the experiment must also be taken into account. 30. The amount of the pure metal ccrtain to be obtained for the ore can be calculated in the following way.
Ex. 11. Translate the sentences into English without using a dictionary.
1. Жидкое состояние, которое, как обычно думают, является промежуточным, проявляет некоторые свойства и твердых всщсств, и газов. 2. Подобно твердым веществам, жидкости являются плотными. 3. Плотность жидкости, как обычно считают, только на 10% меньше плотности твердого вещества. 4. Способность быть растворителем — одно из основных свойств любой жидкости. 5. Представить ссбс молекулярное строение жидкости — одно из важнейших условий понимания природы се свойств.
Ex. 12. Answer the following questions:
1. What arc the main states of matter? 2. What factors determine the properties of liquids? 3. Is there any difference in the density of solids, liquids and gases? 4. Why arc liquids usually thought of as solvents? 5. How can one understand the phenomena associated with the liquid state?
^ Scction II
| Упр. 1. Назовите значения следующих интернациональных слов:
• kinetic, analyse, constantly, collision, observation, botanist, diameter, external, convcction, manifestation, dicrmal, suspend, dctcct, individually, csscncc, cxccutc, energy
Упр. 2. Проверьте, помните ли вы значения следующих слов; если нет, обратитесь к словарю:
substantial, motion, single, neighbour, reveal, tiny, incessant, random, cause, intrinsic, wealth, experience, surround, instant, displace, average
Text 26 В
Прочтите текст про себя (контрольное время чтения — 3,5 минуты). A Kinetic Theory of Liquids
In a liquid, molcculcs arc closc to cach other, and consequently the forccs exerted on one molcculc by its neighbours arc substantial. Thus, the problem of analysing the motion of a single molcculc is exceedingly difficult, for cach is constantly in "collision", subjcct to the forccs for as many as twelve nearest neighbours. What then can wc say about molccular motion in liquids? One of the most revealing observations in this respect was made by the botanist Robert Brown in 1827. Brown discovered that very tiny particles (10"4 cm diameter) suspended in a liquid undergo inccssant randomly directed motion. These motions occur without any apparent external causc such as stirring or convcction, and arc evidently associated with an intrinsic property of all liquids. A wealth of experimental observation has confirmed the idea of this Brownian motion being a direct manifestation of the thermal motion of molcculcs. When it is suspended in a liquid, a very small particlc constantly experiences collisions with all the molcculcs surrounding it. If the particlc is small enough, so few molcculcs will be able to collidc with it, that at any particular instant the number striking it from one side may be different from the number striking it from the other sides; consequently, the particlc will be displaced. Subsequently, another unbalance of collisional forccs may occur, this time displacing the particlc in a different direction. The great majority of these displacements arc so small that they cannot be dctcctcd individually, but the motion which is observed is a result of many of the smaller random displacements. In csscncc, a Brownian particlc is a "molcculc" thought to be large enough to be observable, but small enough to cxccutc observable random thermal motion.
Analysis of the motion of Brownian particles shows that their average kinetic energy is 3/2 kT. Since cach particle is to be considered as one of the molcculcs of the liquid wc can conclude that the average kinetic energy of a molcculc in a liquid is also 3/2 kT — cxactly the same as the kinetic energy of a gaseous molcculc at tfie same temperature.
Упр. 3. Передайте основное содержание текста в нескольких предложениях.
Упр. 4. Какое слово в тексте означает «подвергаться воздействию»?
Упр. 5. Найдите в тексте ответы на следующие вопросы:
1. Почему трудно прослсдить движение одной молекулы жидкости? 2. Как в общем можно охарактеризовать движение молекул жидкости? 3. Как выглядит взаимодействие молекул в жидкости? 4. Как определяется средняя кинетическая энергия молекул жидкости?
Упр. б. Закончите следующие предложения:
1. The molecules in a liquid arc ... 2. To analyse the motion of a single molcculc is difficult bccausc ... 3. Brown discovered ... 4. Brownian motion is causcd ... 5. The average kinetic energy of a molecule in a liquid is ...
Scction Ш
Ex. 1. Make up short dialogues according to the example.
Example: — What's the matter? (What's the trouble?)
— It is cold in this classroom.
— It can't be helped. You'd better go to room 312.
Ex. 2. Respond to the following statements:
1. The molccular motion in a liquid is not easy to describe. 2. Molecules in a liquid arc arranged in a rather orderly manner. 3. The properties of the liquid solvent medium influence the speed of reactions occurring in this medium.
Ex. 3. Give detailed answers to the questions.
1. In what way are liquids and gases alike? 2. In what way do liquids resemble solids? 3. Why are the physical properties of solutions important? 4. What forces act between the molcculcs in a liquid?
Ex. 4. Discuss the following topics:
1. The Liquid State as an Intermediate State Between Solids and Gases.
2. Molccular Motion of Liquids.
3. Properties of Liquids.