Ex. 21. Read the following text and do the exercises.

Kinetic Theory Of Matter

a. Fill in the gaps with the most suitable word

Molecules are the building blocks of _____ and _____ and many ____ as well. Gases, liquids, and solids make up the three states of ______. According to some scientists, plasmas, which are gases, composed of charged particles, make up a _____ _____ of _____. The same substance may be a solid, or a liquid, or a gas, depending upon the ___________. Water, for example, is most familiar to us in the liquid form. When it freezes, it becomes a solid – ____. When it boils, it becomes a gas – _____. What is true of water is true of other _________.

b. Fill in the gaps with the most suitable article

Strictly speaking, then, it is not accurate to call this or that substance ___ solid, or ___ liquid, or ___ gas, because most substances can be found in one or another of ___ states of matter under certain conditions of temperature or pressure. However, most bodies are solids, or liquids, or gases under ordinary conditions, and we refer to them as such. Thus we call iron ___ solid, even though it will melt and become ___ liquid at ___ temperature of 1,535° Celsius. We call carbon dioxide ___ gas even though it can be transformed into ___ solid that we call dry ice.

Molecules are certainly quite unusual building blocks, for they are constantly in motion, except at ___ theoretical temperature that we call absolute zero, ___ equivalent of -273.16° Celsius. ___ laws, governing this motion, have been set in what is known as ___ kinetic theory, or kinetic-molecular theory, of matter. It offers ___ perfectly natural explanation for many phenomena that were once thought to be very mysterious.

c. Fill in the gaps with a suitable preposition

According __ the kinetic theory, the molecules __ a gas __ a container are continually bumping _____ one another and also _____ the walls __ the container. Imagine a half-dozen billiard balls, kept constantly __ motion __ a billiard table. Each ball will move __ a straight line ____ it hits another ball or the side __ the table. ____ such a collision, it will bounce off __ an angle, moving __ a new direction and often ___ a different speed. The gas molecules follow much the same sort __ chaotic pattern, except that they move __ the three dimensions __ space and are not confined to the two dimensions of a table surface. We can see the effect __ this constant movement of molecules __ examining smoke ______ a microscope. We first admit the smoke _____ a closed container which has transparent windows. If we now illuminate the container ____ a bright light and examine it ____ the microscope, we shall be able to see the individual particles __ smoke dancing ____ continually __ an erratic way. The smoke particles move about __ this manner because they are being constantly bombarded __ the molecules __ the gases that make up the air __ the container. The perpetual dance __ particles is called the Brownian movement, or motion, ____ Dr. Robert Brown (1773–1858), a 19th-century Scots scientist, who first showed how general this kind of movement is.

d. Fill in the gaps with the following words

The rate at which the molecules move depends upon the ______ of hotness of a given __________. As a matter of fact, _____ is simply the kinetic _______, or energy of _____, of the molecules of a substance. If there is little heat in a given ________ of gas, the motion of the molecules is slow. If there is more heat, the molecules will dart to and fro more rapidly. They will strike the walls of the container more often and with greater ______.

Date: 2016-01-03; view: 1099