According to Avogadro's principle, equal volumes of gases regardless of composition, contain the same number of molccules at the same temperature and pressure. As a consequence of the principle, the gram- molccular weight of any gaseous substance occupics 22.4 litres at standard temperature (0°C) and pressure (760 mm of mercury). The number of molcculcs per gram-mole has been calculated by different methods of increasing refinement through the years, and is now considered to be 6.023xl0u atoms per gram-atom, or molecules per gram-mole), and it is accurate within 0.1%. For example, one mole of ammonia gas (NHj — weighs 17.073 grams, occupics a volume of 22.4 litre at standard temperature and pressure, and contains 6.023x102* molccules).
At the same temperature, molccules of a liquid move at the same rate as those in a gas. In a liquid, however, the extent of motion must be more restricted. Liquids flow as a stream and tend to form drops to a greater or less extent, thus giving evidence of the importance of the force of cohesion between the molccules in a liquid. Heating liquids, as a rule, results in their expansion, an effect explained by the tendency of the molcculcs to occupy more space when they move at a faster rate. Also, increase in pressure has but slight effect on the volume compressible. From this evidence it is argued that molcculcs in a liquid arc ajacent, close enough to flow in a continuous stream.
The molecules in a liquid, like those in a gas, are not all moving at the same velocity, but at the same average velocity at a given temperature. The molccules at the surfacc of a liquid, unlike those below the surface
layer, have no force of attraction from molcculcs above. Some of the more rapidly moving molcculcs overcome the cohcsivc force of their neighbour and leave the surface. The tendency to leave the surfacc or to evaporate varies from liquid to liquid, and it increases when the temperature is raised. The pressure causcd by the evaporation of molecules from a liquid, measured at equilibrium with the returning molecules at a given temperature, is callcd the vapour pressure. In general, vapour pressure increases when the temperature rises. With continued addition of heat the vapour pressure rises still more until the vapour pressure reaches the vapour pressure of the atmosphere above the liquid. The evaporation goes on throughout the liquid, and the liquid is boiling. Obviously the act of boiling can be accomplished either by raising the temperature of the liquid or by reducing the pressure of the atmosphere above the liquid.
Words and Word-Combinations to Be Memorized
accomplish, ammonia, attraction, average, compress, consequence, equal, equilibrium, evaporation, expansion, extent, fast, flow, go on, layer, litre, mercury, motion, the number of, obviously, occupy, overcome, per, pressure, principle, raise, rate, reducc, regardless of, restrict, result in, return, as a rule, stream, tend, tendency, throughout, unlike, vapour, velocity, weight
Ex. 5. Give the Russian equivalents for the following:
as a consequence of this principle, the gram-molecular weight, calculate by different methods, be accuratc within 0.1 %, move at the same rate, to a greater extent, give evidence of, the force of cohesion, from this evidence, flow in a continuous stream, below the surface layer, overcome the force, rise still more, throughout the liquid, accomplish the boiling, either... or..., 1 reduce pressure
Ex. 6. Give the English equvalents for the following:
равный объем, независимо от состава, одинаковое число молекул, при температуре, под давлением в одну атмосферу, быть ограниченным, в меньшей степени, таким образом, нагревание жидкости, как правило, приводить к, двигаться с большой скоростью, оказывать влияние на, со средней скоростью, при данной температуре, на поверхности жидкости, в отличие от, сила притяжения, тенденция к испарению, достичь атмосферного давления, продолжать нагревание, очевидно, или... или...
Ex. 7. Fill in the blanks with prepositions where necessary.
1. Liquids turn to form drops ... a greater or less extent. 2. One mole ... ammonia gas weighs... 17.073 grams, occupies a volume... 22.4 litres ... standard temperature and pressure. 3. The number ... molecules ... gram-mole was calculated... different methods. 4.... the same temperature,
molcculcs ... a liquid move ... the same rate as those ... a gas. 5. The cffcct ... increasing pressure ... the volume ... a liquid is only slight. 6. The tendency to evaporate varies ... liquid ... liquid. 7. ... general, vapour pressure increases when the temperature rises.
Ex. 8. Translate the sentences into Russian, paying attention to different functions of as.
I. As* conscquencc of Avogadro's principle, it is possible to determine the volume occupicd by the gram-molecular weight of any gaseous substancc at standard temperature and pressure. 2. Molcculcs of a liquid move at the same rate as those in a gas at equal temperatures. 3. Liquids can flow as a stream. 4. As a rule, there is a tendency of the molccules to occupy more spacc when they move at a faster rate. 5. As it was radicr late, they dccidcd to put off their work for the next day. 6. Technically, the process of obtaining oxygen is complicated as it requires one of the lowest temperatures used industrially -194.4°C. 7. As the hydrides of the alkali decompose in water, hydrogen is being released. 8. In the laboratory, hydrogen is made by the reaction of an acid such as sulphuric acid, H2S04, with a metal such as zinc. 9. Mcndclcycv is famous as the discoverer of the law of periodicity. 10. The molcculcs move faster as the temperature rises. 11. The explosion occurcd as the mixture was being heated.
Ex. 9. Translate the sentences into Russian.
1. Discussing the topic helped both of us to understand it better.
2. Working in the laboratory is the most important step in training chemists.
3. Professor N's participating in this confercncc attracted many other scientists. 4. His having made detailed notes at the lecture helped him to successfully pass the examination. 5. Our article being accepted in the Journal of Analytical Chemistry is a great honour to us. 6. There is no saying that the difference in temperature is too great. 7. Learning to work accurately is not an easy task. 8. Sometimes, preparing substances requires less skill than keeping them. 9. There is no denying that application of the quantum theoiy to chemistry stimulated its development. 10. Being very soft is characteristic of both calcium and sodium. 11. Lcbedcv's having prepared synthetic rubber paved the way to the synthesis of other materials. 12. Having examined the results led them to the conclusion that the structure of both compounds was alike. 13. Bohr's being awarded the Nobel prize was an international recognition of his great achievement. 14. Adding small quantitcs of other substances to alloys changes their properties, sometimes to a great extent. 15. Their coming to St. Petersburg was quite unexpected. 16. Investigating the weights and properties of elements led him to the discovery of his world-known law.
Ex. 10. Translate the sentences into English.
1. Закон Авогадро утверждает, что равные объемы различных газов содержат одинаковое количество молекул при одинаковых тсм- пературе и давлении нсависнмо от состава. 2. При одинаковой температуре средние скорости движения молекул жидкости и газа одинаковы. 3. Нагревание тела, как правило, приводит к увеличению его объема. 4. Как у жидкости, так и у газа не все молекулы движутся с одинаковой скоростью при данной температуре. 5. Тенденция к испарению увеличивается, когда повышается температура. 6. Нельзя сказать, что все жидкости испаряются с одинаковой скоростью. 7. Точка кипения жидкости определяется температурой и давлением.
Ex. 11. Answer the following questions:
1. What does Avogadro's principle state? 2. In what way can the number of molcculcs per mole be determined? 3. What forces act between the molcculcs in a gas and in a liquid? 4. What affccts the molecular motion? 5. What process is called evaporation? 6. What is the vapour pressure? 7. What does the boiling point of a liquid depend on?
Section II
Упр. 1. Назовите значения следующих интернациональных слов:
container, limit, crystalline, vibration, oscillation, ciystal, phenomenon, sublimation, dioxide, camphor, sublime, coulomb, graphite, hexagonal, hexagon, associate, fix
Упр. 2. Определите значения выделенных слов по контексту.
1. Water turns into ice at 0°C. 2. The temperature at which a solid changes into a liquid is called its melting point. 3. Repeat the rule several times, then you will remember it. 4. H2S04 is apparently* more complcx s compound than H2S.
Оюва к тексту:
shape—форма; bound — ограничивать; dihedral — образованный двумя плоскостями, гранями; confine — ограничивать; dry — сухой; tie — связывать
Text 17 В
Прочтите текст про себя (контрольное время чтения — 4 минуты). Molecules in Solids
Having their own shape is a characteristic feature of solids since they have their own shape rather than that of the container (as for liquids and gases) and generally do not flow, the extent of molecular motion in a solid is even more limited than that in a liquid. True solids are crystalline, bounded by plane surfaces that meet in a definite dihedral angle, and have a characteristic melting point. The molcculcs in a solid have the same temperature, and if they are molecules of the same
substancc, they arc moving at the same average velocity, the motion of molcculcs in a solid must be confined, and, probably, it is a vibration or oscillation about a fixed point.
Crystals composed of molecules may evaporate in a manner similar to that of liquids. This phenomenon is called sublimation, and it may.be noticed in solid carbon dioxide (dry ice), paradichlorobcnzcnc, camphor, and many odorous solids. Non-molccular solids show little tendency to sublime. The Van dcr Waals force between the particles in molecular solids is, apparently, less in general than the coulomb forces between ions in non-molccular solids. As with liquids, solids vaiy greatly in their tendency to sublime, and the rate of sublimation varies with the temperature and inversely with the pressure. In some solids the ciystal is composed of molecules in a pattern Uiat repeats.
Упр. 3. Передайте основное содержание текста в нескольких предложениях.
Упр. 4. Составьте план текста.
Упр. 5. Прочтите предложения н скажите, соответствуют ли онн содержанию текста. Если нет, исправьте их.
1. Liquids and gases usually have the form of their container.
2. Characteristic feature of solids is that they have their own form.
3. Crystalline solids cannot evaporate like liquids. 4. Sublimation is the evaporation of solids. 5. The rate of sublimation increases with the rise of the temperature and the pressure. 6. Planar structure of the carbon atoms in graphite makes its properties different from those of a diamond.
Упр. б. Найдите в тексте и переведите на русский язык предложения, в которых говорится о движении молекул внутри вещества.
Section Ш
Ex. 1. Answer the questions, using the verb make.
1. When arc you going to make calculations? 2. Who advised you to make this approach to the problem? 3. Have you finished making your measurements? 4. Do you make many mistakes in your English? 5. Don't you remember when Mendeleyev made his greatest discovery? 6.1 think he won't make use of this law and what about you? 7. His lecture made a deep impression on me, and what about you? 8. How long did it take you to make your experiment?
Ex. 2. Translate the sentences into English.
1. Я думаю, необходимо еще раз провести расчеты. 2. Она всегда делает ошибки в чтении. 3. Наш лектор — большой ученый, он сделал важное открытие в физической химии. 4. Сначала вам надо изучить литературу по этому вопросу. 5. Никто не пользуется этим при
бором сейчас, вы можете выполнить свои измерения. 6. Она внссла предложение поехать за город вместе. 7. Он произвел на нас очень хорошее впечатление.
Ex. 3. Make up short dialogues according to the model.
Model: — A request.
| Example: |
— An answr. (+, -)
— Give me your pen, please.
— Here you are. (Sorry, but Vm writing just now.)
Ex. 4. Give detailed answers to the following questions:
1. What is the essence of Avogadro's principle? 2. In what way can Avogadro's principle be used? 3. What do you know about the molecular motion? 4. What is the principal diiTcrcnce between gases, liquids and solids? S. What is the diiTcrcnce in properties between crystalline and non-crystalline solids?
Ex. 5. Discuss the following topics:
1. The Characteristic Features of Gases, Liquids and Solids.
2. The Difference of the Molecular Motion in Various States of a Substancc.
3. The Influence of the Temperature and the Pressure on the State of a Substancc.
WHAT IS IT?
A compound of oxygen and another element (metallic or non-metallic).