English for chemists

Lesson 29
ГРАММАТИКА: Причастие и причастный оборот в функции обстоятель­ ства. Независимый причастный оборот.
Section I
Ex. 1. Practise your reading.
The temperature remaining constant, the fraction of liquid molcculcs with enough kinetic energy to evaporate remains the same, and evaporation continues.
Ex. 2. State what parts of speech the following words belong to:
vapour, vaporous, vaporablc, vaporization, vaporizability, vaporize, evaporate, evaporation, evaporative, evaporator
Ex. 3. Define the meanings of the word until in the following sentences:
1. Continue heating until the solution evaporates completely. 2. Don’t do anything until I comc. 3. Day after day he works until night. 4. Evaporation continues until no liquid is left. 5. It was not until the atomic theory was established that chcmisuy became a nature science founded on scicntific principles. 6. It was not until March 1869 that the paper on the periodic table was presented at the meeting of the Russian chcmical society. 7. Let us wait for him until 9 o’clock and if he doesn’t comc, wc shall go away. 8. There is no suitable technique until now.
Ex. 4. Analyse the following sentence:
The temperature remaining constant, evaporation continues at a constant rate.
Text 29 A
Liquid-Vapour Equilibrium
A liquid of relatively low boiling temperature, when placed in a container open to the atmosphere, will eventually evaporate entirely. Remembering that molcculcs in the liquid arc “bound" by attractive forces to their neighbours, wc might ask why some arc able to overcome these forces and leave the liquid spontaneously. The answer lies in a consideration

1 ОЛ

of the possible magnitudes of molccular kinetic energies, for these, as wc have already mentioned, range from very low to very high values, and arc distributed according to the Maxwcll-Boltzmann law. Therefore, even if the average potential energy which binds the molcculcs to the liquid is substantial, there arc always some molcculcs which have enough kinetic energy to overcome the binding forces and enter the vapour. According to the Maxwcll-Boltzmann law, the fraction of the molcculcs which have kinetic energies greater than some minimum value e, the value required for the molcculcs to leave the liquid, is proportional to the Boltzmann factor, e*t/ir. Therefore, the temperature remaining constant, the fraction of liquid molcculcs with enough kinctic energy to evaporate remains the same, and evaporation continues. The vessel being open to the atmosphere, vapour molcculcs arc swept away, and evaporation continues until no liquid is left.
Now, let us analyse what happens when a liquid is placcd in a closed evacuated container. Immediately, the liquid starts to evaporate at a rate which is primarily determined by the fraction of molcculcs which have enough kinctic energy to overcome attractive forces and leave the surfacc. Initially, the rate of condensation is zero, there being no molcculcs in the vapour. As long as the temperature stays constant, evaporation continues at a constant rate, and the number of molcculcs in the vapour phase increases. Consequently, the rate of condensation starts to increase, for as the pressure of the vapour grows, the number of gas molecules which collidc with and reenter tlic liquid surfacc also increases.
The time dcpcndcncc of the evaporation and condensation rates is worth considering. While growing, the condensation rate eventually bccomcs equal to the rate of evaporation. At this time, the number of molcculcs which enter and which leave the vapour per unit time is the same, and, consequently, the pressure of the vapour stops increasing and remains constant. If the system is left undisturbed at a fixed temperature, evaporation and condensation continue at equal rates, and the pressure of the vapour remains unchanged. This, then, is a situation of equilibrium between the two phases. Note particularly that at equilibrium, evaporation and condensation do not stop, but that the constancy of the equilibrium vapour pressure is a conscqucncc of these opposing processes proceeding at equal rates. Thus wc say that phase equilibrium is dynamic in nature.
Words and Word-Combinations to Be Memorized
analyse, attractive, bind, constant, dependence, initial, magnitude, note, primarily, proportional, situation, spontaneous, substantial, it was not until...

that, not until, vessel, zero

Ex. 5. Give the Russian equivalents Гог the following:
evaporate, entirely, overcome the forces, leave the liquid, the magnitude of the energy, range from... to, substantial, overcome the binding forces, be proportional to, remain the same, start immediately, the dependence is

191

worth considering, bccomc equal to, per unit time, consequently, at a fixed temperature, remain unchanged, opposing processes
Ex. 6. Give the English equivalents for the following:
относительно низкая температура, поместить в сосуд, преодолеть силы притяжения, самопроизвольно, средняя потенциальная энергия, открытый сосуд, давайте проанализируем, начинать испаряться, пер­ воначально, с постоянной скоростью, давление пара растет, положе­ ние равновесия
Ex. 7. Fill in the blanks with articles where ncccssary.
1. Let us analyse what happens when ... liquid is placed in ... closed evacuated container. 2. As long as ... temperature remains constant, ...
evaporation continues a t ... constant rate. 3. As ... pressure o f... vapour grows,... number o f... gas molcculcs returning to ... liquid also increases. 4 time dependence of... evaporation and condensation rates should be considered. S. At equilibrium,... evaporation and condensation do not stop.
Ex. 8. Give synonyms for the following:
magnitude, mention, substantial, fraction, remain, place, primarily, initially, increase, equal
Ex. 9. Give antonyms for the following:
low, open, leave, minimum, the same, continue, container, immediately, start, also, consequently
Ex. 10. Translate the scntcnccs into Russian.
1. Heating the substancc, one must be very attentive. 2. While moving, molcculcs collide with each other. 3. When at the laboratory, one must observe safety rules. 4. Our lecturer being ill, wc had no Iccture yesterday.

5. Our assumption confirmed, wc could continue the experiment. 6. The Iccturc being over, wc shall have a long break for dinner. 7. If present in air in larger amounts than 1 in 20,000 by volume, ozone is irritant and poisonous. 8. Practically, all acids when pure arc polar molccular structures. 9. Having made a number of experiments with calcium and sulphuric acid at the temperature of 40°C, the Russian engineer Petrov was the first to put forward the problem of chcmical activation. 10. One must be very carcful when heating potassium chlorate. 11. Any clement when combining with oxygen forms an oxide. 12. While dealing with chemicals in a laboratory, one can’t do without such apparatus as funnels, beakers and so on. 13. Once discovered, the periodic system of the elements received much scicntific attention. 14. Unless otherwise stated, volumes of gases always refer to standard conditions of temperature and pressure. 15. No substancc can be considered chemically dry unless specially treated. 16. Large pieces of sodium may produce dangerous explosions if plaecd

192

0n water. 17. Sodium hydroxide is prepared industrially by two general jpcthods, the oldest being the reaction of sodium carbonate and calcium hydroxide. 18. Hydrogen peroxide being added to an acidified solution of potassium permanganate, bubbles of gas arc evolved, the gas evolved being oxygen. 19. The formula of a compound being known, wc can calculate its molccular weight. 20. The liquid state being intermediate between the solid and gaseous state, tlic properties of the liquids show similarities to those of both solids and gases. 21. Cobalt and nickel arc much more resistant to atmospheric oxidation than iron, with nickel being especially resistant. 22. Considered from this point of view, the reaction mcchanism seems to depend only on the following three factors. 23. Having analysed the data, the author found that they were in agreement with the theory. 24. Having been heated to I00°C, water began to boil. 25. Having finished the experiment, we must proccss the data. 26. Exccpt where otherwise stated, the measurements were taken at room temperature. 27. Other things being equal, pressure grows proportionately to the temperature. 28. Having discovered the law of periodicity of the chcmical elements, Mendeleyev made his greatest contribution to the development of chcmistry. 29. Studying the properties of any substancc, the chcmist has to perform a number of experiments. 30. Lavoisier (1745-1794), believing oxygen to be a constituent of all acids, gave it the name oxygen (Greek: acid-former).
Ex. 11. Translate the scntcnccs into English without using a dictionary.
1. Если жидкость с низкой температурой кипения находится в открытом сосуде, она в конце концов полностью испарится. 2. Моле­ кулы жидкости связаны с соседними молекулами силами притяже­ ния. 3. Некоторые молекулы обладают достаточной кинетической энергией для того, чтобы преодолеть силы связывания и перейти в пар. 4. При прочих равных условиях, пока температура остается по­ стоянной, испарение продолжается с постоянной скоростью. 5. Если жидкость находится в закрытом сосуде, необходимо рассмотреть про­ цесс конденсации.
Ex. 12. Answer the following questions:

1. 
   What happens with a liquid if it is placcd in an open container?
   

2. 
   What forccs act between the molcculcs in a liquid? 3. Under what conditions can some molcculcs leave the liquid? 4. What happens if a liquid is placcd in a closed evacuated container? 5. What docs the rate of condensation depend upon? 6. What situation is callcd equilibrium between the liquid and vapour phases?