Changes in Matter

Transformations are of two kinds, known as physical and chemical changes. Physical changes are those which affect the state or condition of matter without changing its composition. There is no change in the composition of a substance when it is transformed from the liquid to the gaseous state by heating or from the liquid to the solid state by cooling, and vice versa. Thus, in all three states, steam, water, and ice are all the same substance, made up of the simpler substances, hydrogen and oxygen. The state, but not the composition is affected by the process of heating or cooling.

All matter is made up of atoms. An atom consists of a nucleus containing positively charged protons and neutrons that have no electrical charge. Negatively charged electrons travel around the nucleus. The chemical and physical properties of matter can be explained in terms of electrons, protons, and neutrons. Substances containing only one type of atoms are called elements. When two or more elements are combined in a chemical reaction, a compound is formed. Each compound has its own unique chemical and physical properties. A molecule is made up of two or more atoms. Molecules can be formed by atoms from different elements as well as some atoms form a single element.

By changes in the composition of a substance are meant changes such as when a solid mass is made to fine powder, salt or sugar is dissolved in water. It is clear that such transformations like the changes from one state of matter to another, do not affect the composition of the material. The fine powder of a substance may be made solid again, and we get back the salt or sugar unchanged by evaporating the water.

Chemical changes, however, are those matter changes in which a change of composition does take place and the new substance formed will not return to its original state, unless it is subjected to another chemical change. Thus iron, when it is affected by moist air, is slowly transformed into iron rust entirely different in its properties from the original iron. The new substance will not become iron again when it is allowed to stand, although the iron can be obtained from it if it is subjected to the proper condition.

Thousands of physical and chemical changes take place in nature, and in a laboratory it is possible to cause many other changes artificially which do not occur naturally. For example, by subjecting air to very great pressure and cooling it is possible to transform it to the liquid state – a physical change; while by means of changing the materials which are combined, or the conditions under which they are combined, many substances will be produced by the chemist, some of which are formed in nature while others are not. In observing these transformations, it is important to be able to distinguish between physical and chemical changes.

Exercise 5. Answer the questions.

1. What are the two kinds of transformations described in the text? 2. What do we call physical changes? Give some examples of physical changes. 3. What do changes in the condition of substances mean? 4. What do we call chemical changes? Give some examples of chemical changes. 5. Does a change of composition take place in a chemical change? 6. In what way is it possible to liquefy atmosphere?

Exercise 6.Find synonyms to the following words and translate them into Ukrainian.

change, to consist of, to go back, completely, to permit, to get, to happen, for instance.

Exercise 7. Find antonyms to the words given below and translate them into Ukrainian.

unlike, old, changed, same, solid, artificially, few, rapidly.

Exercise 8. Make up sentences.

1. two, are, of, kinds, there, changes, and, physical, chemical. 2. physical, thousands, place, of, nature, changes, take, in. 3. physical, do, change, transformations, of, not, composition, the, substances.

Exercise 9. Define the tense-form of the predicate and translate the sentences into Ukrainian.

1. When careful studies of the transformation of one form of energy into another had been carried out, the law of the conservation of energy was stated. 2. After the body has been heated, it will get larger in size. 3. By the end of the year all the experiments necessary for the completion of our research will have been made. 4. Before the first human astronaut went into space, much work had been done with the sputniks, carrying dogs and small animals. 5. It has been proved by many experiments that when energy is changed from one form to another the whole amount of energy remains unchanged.

Task III.Read and translate the text.

Text 8B.

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