Thermodynamics

-

Thermodynamics->> FIRST LAW

The first law of thermodynamics gives a precise definition of heat, another commonly used concept.

When an object is brought into contact with a relatively colder object, a process takes place that brings about an equalization of temperatures of the two objects. To explain this phenomenon, 18th-century scientists hypothesized that a substance more abundant at higher temperature flowed toward the region at a lower temperature. This hypothetical substance, called “caloric,” was thought to be a fluid capable of moving through material media. The first law of thermodynamics instead identifies caloric, or heat, as a form of energy. It can be converted into mechanical work, and it can be stored, but is not a material substance. Heat, measured originally in terms of a unit called the calorie, and work and energy, measured in ergs, were shown by experiment to be totally equivalent. One calorie is equivalent to 4.186 × 107 ergs, or 4.186 joules.

The first law, then, is a law of energy conservation. It states that, because energy cannot be created or destroyed—setting aside the later ramifications of the equivalence of mass and energy (see Nuclear Energy)—the amount of heat transferred into a system plus the amount of work done on the system must result in a corresponding increase of internal energy in the system. Heat and work are mechanisms by which systems exchange energy with one another.

In any machine some amount of energy is converted into work; therefore, no machine can exist in which no energy is converted into work. Such a hypothetical machine (in which no energy is required for performing work) is termed a “perpetual-motion machine of the first kind.” Since the input energy must now take heat into account (and in a broader sense chemical, electrical, nuclear, and other forms of energy as well), the law of energy conservation rules out the possibility of such a machine ever being invented. The first law is sometimes given in a contorted form as a statement that precludes the existence of perpetual-motion machines of the first kind.

Comments

Post a Comment

Popular posts from this blog

Berzelius, Jöns Jakob, Baron

-
Berzelius, Jöns Jakob, Baron (1779-1848), Swedish chemist, considered one of the founders of modern chemistry . Berzelius was born near Linköping. While studying medicine at the University of Uppsala, he became interested in chemistry. After practicing medicine and lecturing, he became a professor of botany and pharmacy at Stockholm in 1807. From 1815 to 1832 he was professor of chemistry at the Caroline Medico-Chirurgical Institute in Stockholm. He became a member of the Stockholm Academy of Sciences in 1808 and in 1818 became its permanent secretary. For his contributions to science, Berzelius was made a baron in 1835 by Charles XIV John, king of Sweden and Norway. Berzelius's research extended into every branch of chemistry and was extraordinary for its scope and accuracy. He discovered three chemical elements— cerium , selenium , and thorium —and was the first to isolate silicon , zirconium , and titanium . He introduced the term catalyst into chemistry and was the first to ela
Read more

Hanaoka Seishu

-
Image
A stamp depicting the image of Hanaoka Seishu. Hanaoka Seishu (1760-1835), Japanese physician and pioneer of anesthetic surgery. Hanaoka studied traditional Sino-Japanese medicine, as well as what was then known about Western surgery in Japan. For over two decades he experimented with various drugs. Ultimately he created mafutsusan, an anesthetic compound made from six traditional plant-based drugs, including the alkaloids aconite (from the monkshood plant) and datura (from jimsonweed ). In 1805, using mafutsusan as an anesthetic, Hanaoka removed a tumor during breast cancer surgery. This was the world's first recorded successful surgical operation with anesthesia. Later, Hanaoka used the drug for other surgical operations, developing techniques for bladder stone removal and for amputation. Hanaoka attracted many students, and his surgical techniques became known as the Hanaoka method.
Read more

Mendel’s Laws

-
Mendel’s Laws, principles of hereditary transmission of physical characteristics. They were formulated in 1865 by the Augustinian monk Gregor Johann Mendel . Experimenting with seven contrasting characteristics of pure-breeding garden peas, Mendel discovered that by crossing tall and dwarf parents, for example, he got hybrid offspring that resembled the tall parent rather than being a medium-height blend. To explain this he conceived of hereditary units, now called genes, which often expressed dominant or recessive characteristics. Formulating his first principle (the law of segregation), Mendel stated that genes normally occur in pairs in the ordinary body cells, but segregate in the formation of sex cells (eggs or sperm), each member of the pair becoming part of the separate sex cell. When egg and sperm unite, forming a gene pair, the dominant gene (tallness) masks the recessive gene (shortness). To corroborate the existence of such hereditary units, Mendel went on to interbreed the
Read more