Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Gasoline, mixture of the lighter liquid hydrocarbons used chiefly as a fuel for internal-combustion engines. It is produced by the fractional distillation of petroleum; by condensation or adsorption from natural gas; by thermal or catalytic decomposition of petroleum or its fractions; by the hydrogenation of producer gas or coal; or by the polymerization of hydrocarbons of lower molecular weight.

Gasoline produced by the direct distillation of crude petroleum is known as straight-run gasoline. It is usually distilled continuously in a bubble tower, which separates the gasoline from the other fractions of the oil having higher boiling points, such as kerosene, fuel oil, lubricating oil, and grease. The range of temperatures in which gasoline boils and is distilled off is roughly between 38° and 205° C (100° and 400° F). The yield of gasoline from this process varies from about 1 percent to about 50 percent, depending on the petroleum. Straight-run gasoline now makes up only a small part of U.S. gasoline production because of the superior merits of the various cracking processes.

High-grade gasoline can be produced by a process known as hydrofining, that is, the hydrogenation of refined petroleum oils under high pressure in the presence of a catalyst such as molybdenum oxide. Hydrofining not only converts oils of low value into gasoline of higher value but also at the same time purifies the gasoline chemically by removing undesirable elements such as sulfur. Producer gas, coal, and coal-tar distillates can also be hydrogenated to form gasoline.