Reaction velocity

In many cases heat plays an important role, either starting or accelerating a chemical reaction. In general heat is important under conditions where the reacting substances are all in the gaseous state, or where they are in the liquid state or are all in solution.

In order that atom are molecules should combine and form compounds they must approach so near each other that their attractive forces are great enough to hold them in compounds. Having heated up two reacting gases, we speed up the atoms and molecules; their force of action becomes greater and their union in compounds takes place or is greatly accelerated. It probably is generally known that hydrogen and oxygen gases may be mixed and they will remain together indefinitely at atmospheric pressure without reacting; when, however, their temperature is increased, they will combine forming a compound

Substances in solution or in a liquid form present an ideal case for chemical reactions. The volume is very compact as compared to the gaseous state, and yet the molecules are free to move. They may come easily in contact with each other and combine. In such cases, having increased the temperature, we greatly accelerate the reaction, speeding up the motion of the molecules so that they approach each other with great forces. Lowering the temperature, we slow down the molecular motions, and the speed of reaction is decreased or entirely stopped.

On the other hand, when a gaseous substance is dissolved in a solution, any chemical reaction that might occur between the as and the solution can be slowed down by increasing the temperature.

The speed of a great many reactions may be increased or decreased by what is known as a catalyst. By a catalyst is meant a substance influencing the speed of a chemical reaction but not itself entering into reaction.

COMMENTARY

take place - відбуватися

as compared to - у порівнянні з

are free to move - можуть вільно рухатися

a great many - дуже багато

by what is known as a catalyst - так називаним каталізатором

The story of the electronic microscope

Our story deals with one of the latest developments of modern science, but its origins go about 250 years back in a history

In the early days it was assumed that there was no theoretical limit to the magnifying power of microscopes. It was supposed that as lenses became improved, one could see smaller and smaller objects. However, about seventy years ago it was pointed out that it would never be possible to observe directly an object, which was considerably smaller than the wavelength of the light used to illuminate it.

But, if ordinary light is too coarse, the scientists said, why not use ultraviolet light, it being known that its wavelength is only about one-half that of ordinary blue light? The idea was tried and it worked. By making their lenses of special materials which are transparent to ultraviolet light, the optical experts succeeded in constructing an ultraviolet microscope with a magnification of 2500 diameters. This was more than double the power of the ordinary microscope.

Of course it was natural to think of further extending the method and using still shorter wave lengths, there being many rays beyond the ultraviolet. But this time the physical properties of the rays put a stop to progress. For either the waves were absorbed by the lenses, as was the case with the extremely short ultraviolet rays, or the waves were so penetrating that they passed through the lenses without being affected and focusing the rays become impossible.

Research scientists were becoming more and more aware of the existence of many small structures that could better be studied through a microscope, if only a microscope powerful enough could be built. Probably no one was more surprised than the scientists themselves when the solution came not from students of optics, but from atomic physicists studying electronics.

They found that the electron wavelength is one hundred times as short as that of visible light. The conclusion was obvious. If a microscope could be built to use a beam of electrons in place of the usual beam of light, it would make visible objects far smaller than anything previously seen. It was an exciting idea, which marked the appearance of the new science of electron optics and provided the basic idea for the electron microscope.

A great many electron microscopes are in use today in industrial, medical, and university laboratories. They bring to view the fine structure of every material used in everyday life, being a very useful instrument in the hands of scientists.

COMMENTARY

our story deals with - у нашій розповіді розглядаються

In the early days - спочатку

The idea was tried and it worked - ідея була випробувана і виправдала себе

as was the case - як це було

without being affected - не піддаючи впливу

become aware of - дізнаватися про

useful instrument- корисний інструмент