Chemical Reactions: Evaporation, Redox, and Combustion

Chemicals

Evaporation

Evaporation is a physical process involving a state change from liquid to gas, in which substances can be separated based on their boiling points.

For the transition of a liquid to a gaseous state from liquid surfaces or from the ground, see: Evaporation (hydrology).

Redox

Oxidation-reduction reactions (also known as redox reactions) are electron transfer reactions. This transfer occurs between a set of chemical elements: an oxidant and a reductant (a reduced form and an oxidized form, respectively).

For a redox reaction to occur, the system must contain an element that yields electrons and another that accepts them:

• The oxidizing agent is a chemical element that tends to capture these electrons, resulting in a lower oxidation state.

When a chemical reductant transfers electrons to the medium, it becomes an oxidized element, and its relationship to its precursor is established through what is called a redox couple. Similarly, when a chemical element captures electrons from the medium, it becomes a reduced element and forms a redox couple with its precursor.

Combustion

Combustion is a chemical reaction in which an element (fuel) combines with another (oxidizer, usually oxygen). Combustion is an exothermic reaction that produces:

• Heat
• Light

The most common types of fuel are organic materials containing carbon and hydrogen. The products of these reactions may include carbon monoxide (CO), carbon dioxide (CO2), water (H2O), and ash.

The process of destroying materials by burning is known as incineration.

To initiate the combustion of any fuel, it must reach a minimum temperature, called the ignition temperature or flash point.

There are several types of combustion, including incomplete and complete combustion:

• Incomplete combustion occurs when the fuel does not completely react because there is not enough oxygen. It is recognized by a yellow flame.
• Complete combustion occurs when all the carbon in the burned organic matter is converted into CO2. It can be recognized by the blue flame produced.