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.


Propane, colorless, odorless gas of the alkane series of hydrocarbon. It occurs in crude oil, in natural gas, and as a by-product of petroleum refining. Propane does not react strongly at room temperature. It does react, however, with chlorine at room temperature if the mixture is exposed to light. At higher temperatures, propane burns in air, producing carbon dioxide and water as final products, and is valuable as a fuel.

When it is used as a fuel, propane is not separated from the related compounds, butane, ethane, and propylene. Butane, with boiling point-0.5° C (31.1° F), however, reduces somewhat the rate of evaporation of the liquid mixture. Propane forms a solid hydrate at low temperatures, and this causes great inconvenience when a blockage occurs in a natural-gas line. Propane is used also as so-called bottled gas, as a motor fuel, as a refrigerant, as a low-temperature solvent, and as a source of propylene and ethylene.

Propane melts at -189.9° C (-309.8° F) and boils at -42.1° C (-43.8° F).