Laboratory Exercises

11. Listen and repeat in pauses:

Matter may exist in three fundamental states: solid, liq­uid and gaseous. A solid body has a definite volume and shape. It is difficult to destroy a solid body. A liquid read­ily alters its shape. It maintains its original volume unless subjected to extreme force. A gas has no specific volume and shape.

12. Listen to these questions on the above text and answer them:

1. In what states may matter exist? 2, What does a solid body have? 3. What does a liquid readily alter? 4. What does a liquid maintain?

13. Ask questions using the model,

Model: Water can exist in three states.

What can exist in three states?

1. Heat can change a piece of ice into water. 2. Water

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vapour can be condensed into a liquid. 3. Matter may exist in three states.

14. Listen to this dialogue and learn it by heart :

--Now, comrades, let’s have a talk about three states of matter. What assumptions enables the thrее states of matter to be explained?

— I remember that molecules always possess some mo­tion.

— That's the basis of the kinetic theory. And what about forces of attraction?

— Oh, it's an important assumption too. Molecules exert. forces of attraction on each other.

— Certainly, they do. But when do they exert?

— If they are extremely close to each other.

• You are all right, thanks.

15. Say this in English:

— Какие основные состояния материи вы знаете?

— Я знаю три состояния: твердое, жидкое и газообразное.

— Вода — это жидкость или газ?

— Это жидкость. Ее можно прeвратить в пар, не так ли?

— Конечно. Если вы будете кипятить воду долгое вре­мя, она превратится в пар, Вода имеет свою форму?

— Нет . Oна принимает форму сосуда, в котором содержится.

16. Suggested topics for oral narration:

1. Tell us about assumptions enable the three states of matter to be explained.

2. Give the definition of a) the gaseous state, b) the liquid stale, c) the solid state,

3. What are the three stales of matter? Explain how these three states can be accounted for in terms of attracting molecules possessing kinetic energy.

Additional Material

Read the text and get its central idea. Give titles for logically finished pieces of the text.

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The States of Matter

We live in an ocean of air. There is a great quantity of gas around our planet we call this gas air and experiments show that it is a mixture of several gases -- oxygen, nitrogen, саrbon dioxide, water vapour and others.When we think of the substance which we call water, we commonly think of it as a definite liquid. It doe's not mean, however, that it is the only possible state in which water can exist. The liquid state is the normal state for the substance which we call water, but water can exist also as a gas and as a solid; in the gaseous state it changes to steam or water vapour, and in the solid state it becomes ice. Many substances can and do at various times exist¹ in more than one of these three possible states.

A lump of salt may consist of a number of grains of salt. if we divide the lump into some small parts we still have salt. Further subdivision will in the end bring us to a single grain of salt. We may divide me grain of salt again and again; still the pieces of salt will all have the characteristic of the compound that wе call salt. The last particle which still has the characteristics of the original compound is a molecule of salt. In general, substances consist of molecules; molecules are therefore the building blocks of the physical world, though not the fundamental blocks, for molecules consist of atoms.

There is an equal number of molecules of the same kind in a pound of water as in a pound of steam or in a pound of ice. Why, then, do the various states exist and why do they differ so greatly? The answer to this question lies in the very fact that the molecules move differently in the three states.

In gases we find that the gas molecules are free to move and they are quite far apart. We find that gas molecules move rapidly and continually, spread and occupy every portion of the vessel which contains them. A body of gas there­fore has no definite volume or shape, but takes the volume and shape of the vessel.

A solid, on the other hand, has both volume and shape. The molecules of a solid are also in motion, but they can move only a small amount because the atoms are very close together. The closer the molecules are together, the less free they are to move.

The liquid state is between the gaseous and solid state.

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The molecules of liquid are less free to move than the gas molecules, out are more free to move than the molecules of a solid.

N о t e s

¹ many substances can and do at various times exist -зд. do дано для усиления и следует перенести так: многиe вещества могут существовать и в различное время существуют

² in the very fact — в самом факте

³ are quite far apart — значительно отстоят друг от Друга

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