Примечания к тексту

1. wire [waɪə(r)] – проволока

2. when heated – при нагревании

3. emit [ɪ'mɪt] – испускать

4. retain [rɪ'teɪn] – сохранять

13. Поставьте три вопроса к каждому абзацу текста.

14. Переведите, пользуясь словами и словосочетаниями из текстов А и В:

Плавление, кипение веществ, изменение их формы, нагревание или охлаждение – все эти явления (phenomena) называются физическими. В результате физических изменений состав вещества не меняется.

Такие изменения веществ, в результате которых из одних веществ получаются другие, называются химическими явлениями или химическими реакциями.

В природе химические реакции иногда протекают весьма медленно, поэтому мы их не всегда замечаем.

15. Расскажите на английском языке, в чем заключается разница между физическими и химическими изменениями.

LESSON 7

Грамматика. Условные предложения.

Предтекстовые упражнения

1. Определите тип условного предложения в следующих сложных предложениях и переведите их на русский язык:

1. If a substance cannot be decomposed or produced by combination of other substances, it is called an element. 2. If a gas were colourless, we would not notice its formation. 3. We should have obtained better results if we had used some other materials. 4. Unless the achievements of the scientists of our research Institute had been so great, many of the complex problems would not have been solved. 5. If a substance changes from one state into another, its energy content will change too. 6. If a substance passed from the solid state directly to the vapour state, this change would be called sublimation. 7. You will see a great variety of apparatus if you visit some laboratory. 8. The liquid in the test-tube would change its colour if they raised the temperature. 9. They would have measured the weight of a substance more accurately provided they had taken an analytical balance.

2. Прочитайте и переведите следующие предложения, обращая внимание на выделенные слова:

due to – благодаря

Due to Russian scientist D. I. Mendeleyev elements have been arranged in the order of their atomic weights.

be due to – объясняться, обуславливаться

The change of colour is due to heating.

slightly – слегка

The colour of this liquid changes slightly on heating.

3. Прочитайте и переведите следующие слова, не пользуясь словарем:

component [kəmˈpənənt], gas [gæs], distillation [ˌdɪstɪˈleɪʃ(ə)n], analyse [ˈænəlaɪz], temperature [ˈtemprtʃə], proportion [prəˈpɔːʃ(ə)n], apparatus [ˌæpəˈreɪtəs], nitrate [ˈnaɪtreɪt], barium peroxide [ˈbɛərɪəm pəˈrɒksaɪd]

4. Запомните чтение следующих слов:

air [ɛə], nitrogen [ˈnaɪtrdʒən], physical [ˈfɪzɪkl], occur [əˈk:], infer [ɪnˈf:], vary [ˈvɛərɪ], precisely [prɪˈsaɪslɪ]

Text 7 A

Air

One can prove in several ways that air is not a chemical compound, but a mixture of nitrogen and oxygen with small amounts of other gases.

The composition of air varies slightly with elevation, being a little¹ richer in oxygen and poorer in nitrogen at sea level than at elevations of a few miles. If it were a single² compound, it would have a definite composition by weight.

Air is readily separated into its components by fractional distillation of liquid air. If it were a compound, it would all distil over in a single fraction³ at a definite temperature.

The air that surrounds us is about one fifth oxygen by volume. When cold water is slowly warmed, we see bubbles of “dissolved air” coming out of the solution. If we analyse such bubbles, we shall find that they are about one third oxygen by volume. The change in composition is due to the difference in the solubility of the gases that make up the mixture known as air. If air were a single compound, the bubbles that escape from the solution would have the same composition as those of the undissolved air.

The density and physical properties of air are precisely those that would be inferred from the proportions and physical properties of its component gases. If a chemical change occurred in mixing these gases to form air, there would be either a change in properties or a change in volume.

No chemical formula can be written that would exactly show the proportions in which nitrogen and oxygen are present in air. The nearest simple formula would be N₄O, but this would indicate far too great a density⁴ for air, and the proportion of oxygen in air is slightly greater than this formula indicates.