English for chemists

Section II
Упр. 1. Назовите значення следующих интернациональных слов:
convert, hypothetical, contract, absorption, mole, entropy, compromise, deduce, argument, energetically, chaos, generalization, rationalize, accompany, anticipate
Упр. 2. Проверьте, помните ли вы значення следующих слов; если Нет, обратитесь к словарю:
melt, in turn, stage, involve, represent, extend, evolution, infinitely, likewise, markedly, subtle

199

Text 30 В
Прочтите текст про себя (контрольное время чтения — 3,5 минуты).
Nonideal Solutions
Consider a solid substancc dissolving in a liquid solvent. The solid is such that when melted, it is converted to a liquid that, in turn, can form an ideal solution with the solvent. The dissolution of the solid can be pictured as occurring in two hypothetical stages:
solid solute —» liquid solute —» solute in solution.
The second of these steps docs not involve any energy change, for the solution formed is ideal. In contrast, the first step docs involve the absorption of energy in the amount per mole of solute. Consequently, while the tendency toward maximum entropy favours the dissolution of the solid, the tendency toward minimum energy favours the solid remaining undissolvcd. Therefore, the solubility of the solid is limited, and a saturated solution which represents the best compromise between maximizing entropy and minimizing energy is formed. Since дНГд, is related to the strength of attractive forces between solute molcculcs, wc can dcducc that the magnitudes of these same forces determine the solubility of the solid in ideal solutions.
By using some care, wc can extend our aigumcnts to nonidcal solutions. Two liquids which mix with the evolution of heat will be infinitely soluble in each other, for both energy and entropy ciTccts favour their mixing. Two liquids which mix with the absorption of heat may have limited solubility in each other, for if the mixing proccss is energetically unfavourable, the tcndcncy toward maximum molccular chaos may or may not be sufficient to allow the liquids to mix in all proportions. Likewise, the solubility of a solid is likely to be small if it enters the solution only with considerable absorption of heat. On the other hand, if the dissolution of the solid is accompanied by evolution of heat, the solubility of the solid may be quite high. Even with these generalizations it is difficult to predict or even rationalize qualitatively the solubilities of substanccs that form markedly nonidcal solutions, for the energy and entropy changes that accompany the mixing of strongly irrcacting molcculcs arc subtle and difficult to anticipate.
Упр. 3. Передайте основное содержание текста в нескольких пред­ ложениях.
Упр. 4. Какое слово в тексте означает «представить себе»? Упр. 5. Найдите в тексте ответы на следующие вопросы:

I. What hypothetical steps can be pictured when a melted solid is dissolved? 2. At what stage docs the energy change take place? 3. Why is the solubility of the solid limited? 4. What two liquids will be infinitely soluble in each other? 5. When will the solubility of the solid be high?

200

Упр. 6. Закончите следующие предложения:
1. The magnitudes of the attractive forces determine... 2. Two liquid
will be infinitely soluble in cach other if they mix with... 3. Two liquids

mixing with the absorption of heat may have... 4. It is difficult to predict...

5. If the dissolution of the solid is accompanied by evolution of heat...