Санкт-петербургского государственного университета высшее профессиональное образование т. А. Степанова, И. Ю. Ступина
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1stepanova t a english for chemists
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Scction II I Упр. 1. Назовите значения следующих интернациональных слов: ' kinctic, analyse, constantly, collision, observation, botanist, diameter, external, convection, manifestation, thermal, suspend, dctcct, individually, csscncc, execute, energy Упр. 2. Проверьте, помпнте ли вы значения следу ющих 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 close to each other, and consequently the forces exerted on one moleculc by its neighbours are substantial. Thus, the problem o f analysing the motion o f a single molccule is exceedingly difllcult, for cach is constantly in “collision”, subject to the forces for as many as twelve nearest neighbours. What then can wc say about molccular motion in liquids? One o f the most revealing observations in this respect was made by the botanist Robert Brown in 1827. Brown discovered that very tiny particles (10“* cm diameter) suspended in a liquid undergo inccssant randomly directed motion. These motions occur without any apparent external cause such as stirring or convcction, and arc evidently associated with an intrinsic property of all liquids. A wealth o f experimental observation has confirmed the idea o f this Brownian motion being a direct manifestation o f the thermal motion of molcculcs. When it is suspended in a liquid, a very small particle constantly experiences collisions with all the molcculcs surrounding it. If the particle is small enough, so few molcculcs will be able to collide 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 o f collisional forces may occur, this time displacing the particlc in a different direction. The great majority o f these displacements arc so small that they cannot be detected individually, but the motion which is observed is a result o f many o f the smaller random displacements. In csscncc, a Brownian particlc is a “molccule” 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 J/, kT. Sincc cach particlc is to be considered as one of the molcculcs of the liquid wc can concludc that tlic average kinetic energy of a molcculc in a liquid is also V, kT — exactly the same as the kinetic energy of a gaseous molcculc at tlic same temperature. Упр. 3. Передайте основное содержание текста в исскольких пред ложениях. Упр. 4. Какое слово в тексте означает «подвергаться воздействию»? Упр. 5. Найдите в тексте ответы на следующие вопросы: 1. Почему трудно проследить движение одной молекулы жидко сти? 2. Как в общем можно охарактеризовать движение молекул жид кости? 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 a rc ... 2. To analyse the motion o f a single molcculc is difficult bccausc ... 3. Brown discovered ... 4. Brownian motion is caused ... 5. The average kinetic energy o f a molcculc in a liquid i s ... жүктеу/скачать 5,96 Mb. Достарыңызбен бөлісу:
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