A chemical change in which a substance combines with oxygen is called oxidation, and the substance produced is called an oxide. Combustion is a rapid form of oxidation.
Basic Knowledge
Oxidation is a change in which a substance combines with oxygen, and the product is called an oxide.
Examples of oxidation in everyday life:
・Oxidation of copper: 2Cu + O2 → 2CuO (black copper(II) oxide is formed)
・Combustion of magnesium: 2Mg + O2 → 2MgO (white magnesium oxide)
・Combustion of carbon: C + O2 → CO2
・Combustion of hydrogen: 2H2 + O2 → 2H2O
・Rusting of iron: 4Fe + 3O2 → 2Fe2O3 (iron(III) oxide; slow oxidation)
Combustion is a change involving rapid oxidation while producing light and heat. For combustion to occur, three factors are necessary: a combustible substance, oxygen, and a temperature above the ignition point (the three elements of combustion).
Slow oxidation is oxidation that proceeds slowly without producing heat or light (rusting and rotting).
Oxidation（a chemical change in which a substance combines with oxygen）
Oxide（a substance produced by oxidation. Examples include CuO, MgO, and Fe2O3）
Combustion（rapid oxidation that produces light and heat. The three elements of combustion are necessary）
Slow oxidation（oxidation that proceeds slowly. Rusting and decay）
Three elements of combustion（a combustible substance, oxygen, and a temperature above the ignition point）
Copper oxide（CuO. An oxide of copper. Black）
Further Study
Removing any one of the three elements of combustion puts out a fire. This is the principle of fire extinguishing.
・Pouring water → lowers the temperature (cooling extinguishment)
・Covering with sand → cuts off oxygen (smothering extinguishment)
・Removing the burning substance → removes the combustible material (removal extinguishment)
Copper is reddish-orange, while copper oxide CuO is black. This is why the surface turns black when a copper plate is heated in an experiment. Conversely, when black copper oxide is heated with hydrogen, it returns to reddish-orange (reduction).
Iron rust includes red rust (Fe2O3, brittle) and black rust (Fe3O4, which forms a protective film). Surface treatment that intentionally produces black rust is called black oxide treatment.
- Oxidation = combination with oxygen (an oxide is formed)
- Combustion = rapid oxidation (produces light and heat)
- Slow oxidation = slow oxidation (rusting and rotting)
- Three elements of combustion = a combustible substance, oxygen, and a temperature above the ignition point
- Oxidation of copper:
2Cu + O2 → 2CuO(black) - Combustion of Mg:
2Mg + O2 → 2MgO(white) - Fire extinguishing = removing one of the three elements
Points to Note
① Combustion and oxidation: combustion is a type of oxidation, but not all oxidation is combustion. Rusting (slow oxidation) is not combustion. ② Oxide and oxidation: an oxide is a substance formed by oxidation, while oxidation is the name of a change. ③ Remember that CuO formed by copper oxidation is black (MgO is white). ④ The principle of fire extinguishing is the removal of one of the three elements of combustion; be sure to remember all three elements.
Practice
- State all three elements of combustion.
- Write the chemical equation for the chemical change that occurs when copper is heated. Also, from what color to what color does copper change?
- Give two familiar examples of slow oxidation.