3 Part One. The Predicate

Molecules in Gases and Liquids
According to Avogadro’s principle, equal volumes of gases regardless of composition, contain the same number of molecules at the same temperature and pressure. As a consequence of the principle, the gram- molecular weight of any gaseous substance occupies 22.4 litres at standard temperature (0°C) and pressure (760 mm of mercury). The number of molecules per gram-molc has been calculated by different methods of increasing refinement through the years, and is now considered to be 6.023x10²³ atoms per gram-atom, or molecules per gram-molc), and it is accurate within 0.1%. For example, one mole of ammonia gas'(NH₃) — weighs 17.073 grams, occupies a volume o f 22.4 litre at standard temperature and pressure, and contains 6.023x10²³ molecules).

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 o f the importance of the force of cohesion between the molecules in a liquid. Heating liquids, as a rule, results in their expansion, an effect explained by the tendency of the molecules to occupy more space when they move at a faster rate. Also, increase in pressure has but slight cffcct on the volume compressible. From this evidence it is argued that molecules in a liquid are ajaccnt, 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 molecules at the surface of a liquid, unlike those below the surface layer, have no force of attraction from molecules above. Some o f the more rapidly moving molecules 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 caused by the evaporation o f molecules from a liquid, measured at equilibrium with the returning molecules at a given temperature, is called 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 Uzbek equivalents for the following:

as a consequence of this principle, the gram-molecular weight, calculate by different methods, be accurate within 0.1 %, move at the same rate, to a greater extent, give cvidcncc of, the force of cohesion, from this cvidcncc, flow in a continuous stream, below the surface layer, overcome the force, rise still more, throughout the liquid, accomplish the boiling, either... or...,

* reduce pressure
Ex. 6. Give the English equvalents for the following:

Tarkibidan qat'i nazar, teng miqdordagi molekulalar soni, bitta atmosferada bosim ostida bo'lgan harorat kamroq darajada cheklangan bo'ladi, shuning uchun suyuqlikni isitish, qoida tariqasida, yuqori tezlikka olib keladi, ta'sir qiladi. tezligi, ma'lum bir haroratda, suyuqlik yuzasida, tortishish kuchidan farqli o'laroq, bug'lanish, atmosfera bosimiga ko'tarilish, qizdirishni davom ettirish, shubhasiz, yoki ... yoki ...

Ex. 7. Fill in the blanks with prepositions where n ecessary .

1. Liquids turn to form drops ... a greater or less extent. 2. One mol... ammonia gas weighs... 17.073 grams, occupics a volume... 22.4 litres ... standard temperature and pressure. 3. The number ... molecules ... gram-molc was calculated... different methods. 4 .... the same temperature,molecules ... a liquid move ... the same rate as those ... a gas. 5. The effect ... 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 Uzbek, paying attention to different functions of as.

1. A sa consequence of Avogadro’s principle, it is possible to determine the volume occupied by the gram-molecular weight of any gaseous substance at standard temperature and pressure. 2. Molecules of a liquid move at the same rate asthose in a gas at equal temperatures. 3. Liquids can flow asa stream. 4. Asa rule, there is a tendency of the molecules to occupy more space when they move at a faster rate. 5. Asit was rather late, they decided to put off their work for the next day. 6. Technically, the process of obtaining oxygen is complicated asit requires one of the lowest temperatures used industrially -194.4°C. 7. Asthe 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 assulphuric acid, H₂SO₄, with a metal such aszinc. 9. Mendeleyev is famous asthe discovercr of the law of periodicity. 10. The molecules move faster asthe temperature rises. 11.ТЪе explosion occured asthe mixture was being heated.

Ex. 9. Translate the sentences into Uzbek.

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 conference 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 o f Analytical Chemistryis 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 theory to chemistry stimulated its development. 10. Being very soft is characteristic of both calcium and sodium. 11. Lebedev’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 quantites 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. Avogadro qonunida aytilishicha, har xil gazlarning teng miqdordagi tarkibi qanday bo'lishidan qat'iy nazar, bir xil harorat va bosimda bir xil miqdordagi molekulalar mavjud. 2. Xuddi shu haroratda suyuqlik va gaz molekulalarining o'rtacha tezligi bir xil. 3. Jismni qizitish, qoida tariqasida, uning hajmini oshirishga olib keladi. 4. Suyuqlik ham, gaz uchun ham barcha molekulalar ma'lum bir haroratda bir xil tezlikda harakat qilmaydi. 5. Bug'lanish tendentsiyasi harorat ko'tarilganda ortadi. 6. Barcha suyuqliklar bir xil tezlikda bug'lanadi, deyish mumkin emas. 7. Suyuqlikning qaynash nuqtasi harorat va bosim bilan belgilanadi.

Ex. 11. Answer the following questions:

1. What does Avogadro’s principle state? 2. In what way can the number of molecules per mole be determined? 3. What forces act between the molecules in a gas and in a liquid? 4. What affects 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?