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EXERCISES

VOCABULARY

AND THE STATES OF MATTER

THE MOLECULAR THEORY OF MATTER

Molecules are too small and are not seen under the most powerful microscope, but the movement of molecules can be made more real by a study of the so-called Brownian movement. Robert Brown, a botanist, observed in 1827 that small solid particles suspended in a liquid were in continual movement. In fact the chief characteristic of matter is its eternal restlessness, and the degree of restlessness is determined by the state of matter under observation; i.e. whether it is solid, liquid or gas. In gases molecules lead more or less independent existence and are moving with high speed in all directions; and the molecules must be continually colliding with each other and striking the walls of the vessel, and so exert pressure. A gas, therefore, has no definite shape or volume, and can be readily compressed. The molecules of a liquid can move sufficiently freely and allow the liquid to take up the shape of the vessel; but the attractive forces between the molecules, which are much closer together and moving more slowly than in a gas, do not permit the liquid to be compressed to any extent nor to vary its volume. A liquid, therefore, has a definite volume but not fixed shape, and is slightly compressible. In solids the freedom of the molecules must be very restricted and their motion is probably confined to small oscillations only, and must be greatly hampered by the nearness of neighbouring molecules. A solid, therefore, has both definite shape and volume, and is very difficult to compress. The rates of motion of molecules have an important influence on chemical changes. They occur most readily when molecules are moving freely, i.e. in gases; and chemical activity is least pronounced in solids, where the movement of molecules is slight.

confine - обмежувати neighbouring - сусідній continual – безперервний, постійний observe- спостерігати hamper - ускладнювати оссur – траплятися, мати місце oscillation - коливання hardly - ледве pressure - тиск probably - можливо slight - незначний readily - легко suspend- вішати, підвішувати restlessness - рухомість therefore - відповідно vessel - посудина restricted – обмежений

1. How can the movement of molecules be studied?

2. Why does gas have neither definite shape nor volume?

3. Why is liquid slightly compressible?

4. Why is the freedom of molecules in solids very restricted?

5. Why is it very difficult to compress a solid?

6. In what substances do chemical changes occur most readily?

2. Give English equivalents:

1. потужний мікроскоп а. under observation

2. постійний рух b. independent existence

3. під наглядом c. high speed

4. незалежне існування d. continual movement

5. велика швидкість e. powerful microscope

3. Give Ukrainian equivalents:

1. with each other а. сила тяжіння

2. to exert pressure b. змінювати об’єм

3. the attractive force c. постійна форма

4. to vary one's volume d. чинити тиск

5. a fixed shape e. один з одним

4. Translate the sentences:

1. Matter is constantly undergoing changes. 2. The concept of matter is intuitive and yet it is somewhat difficult for definition. 3. Forms of matter may change, but matter itself is neither destroyed nor created. 4. Newton's Law of universal gravitation is applied to matter in general. 5. About 90% of the matter of the Sun is hydrogen. 6. Matter is now regarded as being discontinuous. 7. Matter occupies space and it possesses mass. 8. Temperature is an intensive property; it doesn't matter how much substance is present. 9. As a matter of fact Robert Brown observed the movement of small solid particles in liquid quite unexpectedly. 10. Gas has no definite shape or volume. No matter what vessel it is placed in, the whole space of the vessel is occupied by gas. 11. The effect of continual movement of small solid particles suspended in a liquid is referred to as Brownian movement.1 2. His discovery is referred to in every text-book on physics. 13. This phenomenon is referred to as pressure exerted by gas. 14. The results of their experiments were referred to at the conference.


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