catalysis \ko-'ta-b-s3s\ Modification (usually acceleration) of a chemi¬ cal reaction rate by addition of a catalyst, which combines with the reac¬ tants but is ultimately regenerated so that its amount remains unchanged and the chemical equilibrium of the conditions of the reaction is not altered. Catalysts reduce the activation energy barrier between reactants and prod¬ ucts. When more than one reaction is possible, a catalyst that accelerates only one reaction pathway selectively enhances the creation of its prod¬ uct. Catalysis is inhibited if the reactant or the catalyst is removed or altered by any of several types of agents (inhibitors). Catalysis in a single phase (e.g., the catalyst is dispersed in a liquid solution or gaseous mix¬ ture with the reactants) is homogeneous; that in more than one phase (e.g., the reactants are liquids and the catalyst a solid) is heterogeneous. Chemi¬ sorption, a type of heterogeneous catalysis, often involves bonding between the catalyst’s solid surface and the reactant, changing the nature of the chemisorbed molecules. To make the accessible surface area as large as possible, such catalysts are finely powdered or highly porous sol¬ ids. Catalysis is essential to the modern chemical industry. See also enzyme.
catalyst \'ka-t 3 l-3st\ Any substance of which a small proportion nota¬ bly affects the reaction rate of a chemical reaction without itself being changed or consumed (see catalysis). One molecule may transform sev¬ eral million reactant molecules a minute. Catalysts may be gaseous, liq¬ uid, or solid; they may be inorganic compounds, organic compounds, or complex combinations. They tend to be highly specific, reacting with only one substance or a small set of substances. Substances that reduce the effectiveness of catalysts by altering them or blocking reactants’ access to them are called catalyst inhibitors or catalyst poisons. Catalysts are essential to virtually all industrial chemical reactions, especially in petro¬ leum refining and synthetic organic chemical manufacturing. Most solid catalysts are transition elements (metals) or their oxides in finely divided or porous form. In a car’s catalytic converter, the platinum catalyst con¬ verts unburned hydrocarbons and nitrogen compounds to products less harmful to the environment. Water, especially saltwater, catalyzes oxida¬ tion (see oxidation-reduction) and corrosion. Enzymes are among the most active and selective catalysts known.
catalytic converter In automobiles, a component of emission control systems used to reduce the discharge of noxious gases from the internal- combustion engine. The catalytic converter consists of an insulated cham¬ ber containing pellets of catalyst through which the exhaust gases are passed. The exhaust’s hydrocarbons and carbon monoxide are converted to water vapour and carbon dioxide.
catamaran Vka-to-mo-.ranV Twin-hulled sailing and engine-powered boat. Its design was based on a raft of two logs bridged by planks used by peoples in the Indonesian archipelago, Polynesia, and Micronesia. Up to 70 ft (21 m) long, early catamarans were paddled by many men and used for travel, in war, and in recreation. Especially after the sail was added, voyages as long as 2,000 mi (3,700 km) were made. In the 1870s they sailed so successfully against monohulled boats that they were barred
from racing. The modern catamaran, which averages about 40 ft (12 m) in length, has been produced since 1950. They are very fast craft, achiev¬ ing speeds of 20 mph (32 kph).
Catania \ka-'ta-nya\ City (pop., 2001 prelim.: 306,464), Sicily, Italy. It was founded by Greeks in 729 bc at the foot of Mount Etna on the Gulf of Catania. Taken by the Romans in the First Punic War (263 bc), Cata¬ nia was made a Roman colony by Octavian (later Augustus). Catanian Christians suffered under the emperors Decius and Diocletian; their mar¬ tyrs included St. Agatha, patron saint of the city. Catania fell successively to the Byzantines, Arabs, and Normans, and it suffered devastation by earthquakes especially in 1169 and 1693. In World War II the city was severely damaged by bombing. Rebuilt, it is Sicily’s second largest city and is an industrial and transportation centre.
Catanzaro \,ka-tand-'za-r6\ City (pop., 2001 prelim.: 93,540), capital of Calabria, southern Italy. Catanzaro lies near the Gulf of Squillace. It was probably founded in the 10th century by Byzantines. It was taken in 1059 by the Normans under Robert Guiscard. It played an important part in the Napoleonic Wars and in the movement for Italian unity. Catanzaro suffered severely from earthquakes in 1905 and 1907 and from bombing in World War II. It is an agricultural centre.
catapult Mechanism for forcefully propelling stones, spears, or other projectiles, in use since ancient times. Nearly all catapults employed in ancient and medieval artillery operated by a sudden release of tension on wooden beams or twisted cords of horsehair, gut, sinew, or other fibres. An exception was the medieval trebuchet, powered by a counterweight. Modem mechanisms using steam, hydraulic pressure, tension, or other force to launch gliders, aircraft, or missiles are also called catapults.
cataract Opacity of the eye’s crystalline lens. Cataracts causing central visual-field defects are most likely to affect vision. Cataracts may occur in newborns and infants. Diabetes mellitus, prolonged exposure to ultravio¬ let rays, or trauma can cause them in adults, but they most often occur with age, resulting from gradual loss of transparency of the lens. Treat¬ ment is a surgical procedure to replace the lens with an artificial one.
catastrophe theory Branch of mathematics (considered a branch of geometry) that explores how gradual changes to a system produce sud¬ den, drastic results (though usually not as dire as the name suggests). A simple example is how a plastic coffee stirrer subjected to gradually increasing pressure from both ends will suddenly buckle in one direction or another. Other “catastrophes” include optical phenomena such as reflection or refraction of light through moving water. More speculatively, ideas from catastrophe theory have been applied by social scientists to such situations as the sudden eruption of mob violence.
Catatumbo \,ka-ta-'tum-bo\ River River, northern South America. Rising in northern Colombia, it flows northeast across the Venezuelan border and the oil-rich Maracaibo lowland to empty into Lake Maracaibo after a course of 210 mi (338 km).
Catawba Vko-'to-bsN North American Indian people of South Carolina, U.S. The meaning of the name Catawba, which seems to have been applied after European contact to several small bands of peoples in the region of the Catawba River, is unknown. The peoples first encountered by Hernando de Soto subsisted principally by farming, harvesting com, beans, squash, and gourds. Fish and birds were also staples of their diet. They traded bowls, baskets, and mats to other native groups and, later, to colonists. Each village was governed by a council presided over by a chief. After contact with European settlers, disease and other factors diminished their numbers rapidly. In the 2000 U.S. census some 1,700 people identified themselves as of sole Catawba descent.
Catawba River River, southeastern U.S. Rising in North Carolina’s Blue Ridge, it flows south into South Carolina, where it becomes the Wateree River. It is 220 mi (350 km) long. With the Wateree, it forms an important source of hydroelectric power for South Carolina.
catbird Any of several passerine species (family Mimidae) named for their mewing calls, which they use in addition to song. The North Ameri¬ can catbird ( Dumetella carolinensis) is 9 in. (23 cm) long and gray with a black cap. It is found in gardens and thickets. The black catbird ( Mel- anoptila glabrirostris) is found in coastal Yucatan. Three species of the bowerbird family are also called catbirds; they are found in Australia, New Guinea, and nearby islands and do not build bowers but hold territories in the forest by loud singing.