This represents one extreme limit of a continuous range of possibilities. At… The prediction and measurement of the heat effects that accompany chemical changes are important to the understanding and use of chemical reactions. If the vessel containing the reacting system is so insulated that no heat flows into or out of the system adiabatic conditionthe heat effect that accompanies the transformation may be manifested by an increase or a decrease in temperature, as the case may be, of the substances present.
The 20th century Technology from to Recent history is notoriously difficult to write, because of the mass of material and the problem of distinguishing the significant from the insignificant among events that have virtually the power of contemporary experience.
In respect to the recent history of technology, however, one fact stands out clearly: The airplane, the rocket and interplanetary probes, electronics, atomic power, antibiotics, insecticides, and a host of new materials have all been invented and developed to create an unparalleled social situation, full of possibilities and dangers, which would have been virtually unimaginable before the present century.
In venturing to interpret the events of the 20th century, it will be convenient to separate the years before from those that followed. The years to were dominated by the two World Wars, while those since were preoccupied by the need to avoid another major war.
The dividing point is one of outstanding social and technological significance: There were profound political changes in the 20th century related to technological capacity and leadership. It was a rise based upon tremendous natural resources exploited to secure increased productivity through widespread industrialization, and the success of the United States in achieving this objective was tested and demonstrated in the two World Wars.
Technological leadership passed from Britain and the European nations to the United States in the course of these wars. This is not to say that the springs of innovation went dry in Europe. Many important inventions of the 20th century originated there.
But it was the United States that had the capacity to assimilate innovations and take full advantage from them at times when other countries were deficient in one or other of the vital social resources without which a brilliant invention cannot be converted into a commercial success.
As with Britain in the Industrial Revolutionthe technological vitality of the United States in the 20th century was demonstrated less by any particular innovations than by its ability to adopt new ideas from whatever source they come. The two World Wars were themselves the most important instruments of technological as well as political change in the 20th century.
The rapid evolution of the airplane is a striking illustration of this process, while the appearance of the tank in the first conflict and of the atomic bomb in the second show the same signs of response to an urgent military stimulus.
In other respects the two wars hastened the development of technology by extending the institutional apparatus for the encouragement of innovation by both the state and private industry. This process went further in some countries than in others, but no major belligerent nation could resist entirely the need to support and coordinate its scientific-technological effort.
While the extent of this transformation must not be overstated, and recent research has tended to stress the continuing need for the independent inventor at least in the stimulation of innovation, there can be little doubt that the change in the scale of technological enterprises had far-reaching consequences.
It was one of the most momentous transformations of the 20th century, for it altered the quality of industrial and social organization. In the process it assured technology, for the first time in its long history, a position of importance and even honour in social esteem.
Fuel and power There were no fundamental innovations in fuel and power before the breakthrough ofbut there were several significant developments in techniques that had originated in the previous century. An outstanding development of this type was the internal-combustion enginewhich was continuously improved to meet the needs of road vehicles and airplanes.
The high-compression engine burning heavy-oil fuels, invented by Rudolf Diesel in the s, was developed to serve as a submarine power unit in World War I and was subsequently adapted to heavy road haulage duties and to agricultural tractors.
Moreover, the sort of development that had transformed the reciprocating steam engine into the steam turbine occurred with the internal-combustion engine, the gas turbine replacing the reciprocating engine for specialized purposes such as aero-engines, in which a high power-to-weight ratio is important.
Admittedly, this adaptation had not proceeded very far byalthough the first jet-powered aircraft were in service by the end of the war. But the construction of a satisfactory gas-turbine engine was delayed for a decade by the lack of resources, and particularly by the need to develop new metal alloys that could withstand the high temperatures generated in the engine.
This problem was solved by the development of a nickel-chromium alloy, and, with the gradual solution of the other problems, work went on in both Germany and Britain to seize a military advantage by applying the jet engine to combat aircraft.
Gas-turbine engine The principle of the gas turbine is that of compressing and burning air and fuel in a combustion chamber and using the exhaust jet from this process to provide the reaction that propels the engine forward.
In its turbopropeller form, which developed only after World War IIthe exhaust drives a shaft carrying a normal airscrew propeller. Compression is achieved in a gas-turbine engine by admitting air through a turbine rotor. In the so-called ramjet engine, intended to operate at high speeds, the momentum of the engine through the air achieves adequate compression.
The gas turbine has been the subject of experiments in road, rail, and marine transport, but for all purposes except that of air transport its advantages have not so far been such as to make it a viable rival to traditional reciprocating engines.
Petroleum As far as fuel is concerned, the gas turbine burns mainly the middle fractions kerosene, or paraffin of refined oil, but the general tendency of its widespread application was to increase still further the dependence of the industrialized nations on the producers of crude oilwhich became a raw material of immense economic value and international political significance.
The refining of this material itself underwent important technological development.
Until the 20th century it consisted of a fairly simple batch process whereby oil was heated until it vaporized, when the various fractions were distilled separately.
Apart from improvements in the design of the stills and the introduction of continuous-flow production, the first big advance came in with the introduction of thermal cracking.A chemical reaction is a process where a set of substances undergo a chemical change to form a different substance.
Where do chemical reactions occur? You may think that chemical reactions only happen in science labs, but they are actually happening all the time in the everyday world. > Global Challenges. Our expertise and global reach help promote safety and health for the planet and its inhabitants.
> Strategic Priorities Our focus revolves around Agriculture & Nutrition, Advanced Materials and Bio-Based Industrials. Chemical reactions are important because they are the basis of all life on earth.
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