Autocross is a form of motorsports that emphasizes safe, low-cost competition and active participation. Rather than racing wheel-to-wheel, as in road racing or oval racing, an autocross is a timed competition where drivers navigate through a temporary course marked by traffic cones. Autocross tends to place more emphasis on car handling and driver skill than on sheer horsepower and events typically have many classes which allow almost any vehicle, from grocery-getters to specially-prepared race cars, to compete. Speeds are slower in absolute terms when compared to other forms of motorsports, usually not exceeding highway speeds, but the activity level (measured in driver inputs per second) can be higher than even Formula One due to the large number of elements packed into each small course[citation needed]. In addition to being a national-level motorsport in its own right, autocrossing is a great way to get started in road racing.

Autocross events are usually held in large paved areas like parking lots or airfields. Typically, new courses are created for each event so drivers must learn a new course each time they compete. Prior to driving, a competitor will walk the course, taking mental notes, and developing a strategy to be refined upon subsequent runs. Organizations such as the SCCA and NASA sponsor autocross events throughout the United States, and many areas have independent autocross clubs. Automobile manufacturers and their associated clubs (e.g. the BMW Car Club of America) sometimes hold marque autocross events.

Chemical reaction
A Chemical reaction is a process that results in the interconversion of chemical substances. Such reactions can result in molecules attaching to each other to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. For example, substances that react with oxygen to produce other substances are said to undergo oxidation; similarly a group of substances called acids or alkalis can react with one another to neutralize each other's effect, a phenomenon known as neutralization. Substances can also be dissociated or synthesized from other substances by various different chemical processes.