Exercises

1. Answer the questions

1. When are the molecules able to break out of the lattice?

2. When does the substance lose its definite shape?

3. Why do liquids give off smell?

4. What happens when a liquid is heated?

5. What is evaporation?

6. What is condensation?

2. Give synonyms:

essential, universal, to cause, liquid, to deposit, fluid, to make, general, principal, to

precipitate.

3. Give antonyms:

to cool, eventually, to supply, to attract, boiling point, to repell, to provide, at last, to

heat, freezing point

4. Translate the following sentences:

1. Molecules are in constant motion, the motion becoming more rapid with the increase of temperature. 2. The temperature being raised, the kinetic energy is increased. 3. The evaporation increases with the temperature, other conditions being equal. 4. Water power being one of the best and cheapest ways of producing electricity, it is widely utilized to drive generators which provide electric current. 5. This material being used in electronics, its properties should be studied closely. 6. Non-metallic materials are of great importance, some of them being widely used in place of metals. 7. They have to compare their experiments, their results being different. 8. The data having been obtained, we discussed the results at the conference. 9. Water being heated, it boils at 100°C. 10. The molecules of the solid when heated break out of the lattice, the solid melting. 11. Gaining enough energy to move far apart, the molecules often collide with the sides of the container they are in. 12. The students investigating this phenomenon carry out the experiments in the laboratory of general chemistry. 13. Breaking out of the lattice the molecules of the solid gain enough energy, being free to move. 14. The experiment being carried out by the researcher deals with the liquid state of matter. 15. Having prepared everything for the experiment, they reviewed once more the theoretical back- ground for its fulfillment.

WATER

Water plays the most essential part in our lives. It is universally needed, but it is not naturally present everywhere. Where does water come from? We know that the evaporation of water from rivers and from the sea causes the water vapour to be held in the atmosphere, from which, on cooling, it is deposited as rain. This rain eventually finds its way back to the rivers and sea and so the cycle begins all over again. The heat of the sun supplies the energy for the evaporation.

Rain-water is not chemically pure, although it is the nearest approach to a pure water among natural waters. Containing little or no mineral matter, it does contain dissolved gases. Water was originally thought to be an element; it was produced by both Priestley and Cavendish by passing a spark through a mixture of hydrogen and oxygen in the proportions of two volumes to one; Lavoisier showed water to be a compound. Water itself may be prepared in the laboratory by burning hydrogen in oxygen or in air, or by passing an electric spark through a mixture of oxygen and hydrogen: 2H2 + 02 = 2H20.