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Physical and Chemical Changes
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A physical change involves no change in chemical composition. Cutting a piece of aluminium foil into small pieces is one example; changing a substance from one physical state to another is a second example. When solid water (ice) melts or liquid water boils, none of the H2O molecules change; instead, the molecules form different spatial (physical) patterns. In a chemical change or chemical reaction, the chemical compositions of the elements or compounds alter.
Chemists use short chemical equations to represent what happens in a chemical reaction. A chemical equation shows the chemical formulae for the reactants (initial chemicals) and the products (chemicals produced) with an arrow between them. For example, when coal burns completely, the solid carbon (C) which it contains combines with oxygen gas (O2) from the atmosphere to form the gaseous compound carbon dioxide (CO2):
Reactant(s) Product(s)
carbon + oxygen carbon dioxide + energy
C + O2 CO2 + energy
This reaction gives off energy and makes coal a useful fuel. The reaction also shows how the burning of coal adds carbon dioxide gas to the atmosphere.
Physical and chemical changes illustrate the connections between matter and energy. Any physical or chemical change either requires or gives off energy. For example, it takes energy to convert liquid water to steam. However, when the steam contacts a cooler object (such as your skin), it releases energy and returns the water to its liquid state – which is why steam can cause severe burns.
II. Read the following international words and give their Russian equivalents.
Composition, aluminium, second, to alter, to organize, reaction, composition, product, to contain, atmosphere, to illustrate, to convert, to contact.
III. Fill in the table.
| Verb | Noun | Adjective |
| differ | ||
| reaction | ||
| connect | ||
| change | ||
| illustrative |
IV. Match synonyms.
| 1. give off 2. change 3. connect 4. show 5. example | a. pattern b. combine c. release d. alter e. illustrate |
V. Underline the odd word in each group. Explain the choice.
| a. solid a. ice a. substance a. to contact | b. gas b. steam b. material b. to convert | c. atom c. water c. compound c. to change | d. liquid d. carbon d. matter d. to alter |
VI. Mark the statements as true (T) or false (F). Correct the false statements.
1. A physical change involves many changes in chemical composition.
2. Any physical or chemical change neither requires nor gives off energy.
3. When the steam contacts a cooler object, it releases energy.
4. Physical and chemical changes illustrate the connections between matter and energy.
VII. Answer the following questions to the text.
1. Does a physical change involve a change in chemical composition? Give examples.
2. What do we call a chemical reaction?
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3. What happens during the chemical reaction?
4. What does a chemical reaction show?
5. What happens in converting liquid water to steam?
VIII. Rearrange the following sentences to make the summary of the text.
1. Any physical or chemical change either requires or gives off energy.
2. The chemical formulae of the reactants and the products with an arrow between them are called chemical equation.
3. A chemical change or reaction alters the chemical compositions of the elements.
4. A physical change does not change chemical composition.
5. Physical and chemical changes illustrate the connections between matter and energy.
Unit 6
Tenses in the Active Voice
Vocabulary
although – хотя
amount (n.) – количество
billion (num.) – миллиард
bury (v.) – хоронить, зарывать в землю, прятать
carry (v.) – переносить
conservation (n.) – сохранение
consume (v.) – потреблять
create (v.) – создавать
destroy (v.) – уничтожать
discard (v.) – выбрасывать
dust (n.) – пыль
earth (n.) – земля
emit (v.) – испускать, выделять
environment (n.) – окружающая среда
essentially (adv.) – существенно, по существу, чрезвычайно
evolve for (v.) – эволюционировать, превращаться в, развивать(ся)
gain (n.) – прибыль, прирост
hence – следовательно
key chemicals – ключевые химические продукты
law (n.) – закон
loss (n.) – потеря
mean (v.) – значить, означать
measurement (n.) – измерение
minute (adj.) – мелкий, мельчайший
occasional (adj.) – случайный
process (v.) – обрабатывать, перерабатывать
receive (v.) – получать
resource (n.) – ресурс, источник
soil (n.) – почва
term (n.) – термин
throw (threw, thrown) (v.) – бросать
I. Read and translate the text.
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