|Jmol-3D images||Image 1|
|Molar mass||56.0774 g/mol|
|Appearance||White to pale yellow/brown powder|
2613 °C, 2886 K, 4735 °F
|Solubility in water||1.19 g/L (25 °C), 0.57 g/L (100 °C), exothermic reaction|
|Solubility in acids||soluble (also in glycerol, sugar solution)|
|Solubility in methanol||insoluble (also in diethyl ether, n-octanol)|
|Std enthalpy of
|EU Index||Not listed|
|Other anions||Calcium sulfide
|Other cations||Beryllium oxide
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)|
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature. The broadly used term "lime" connotes calcium-containing inorganic materials, which include carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate, such as limestone. By contrast, "quicklime" specifically applies to a single chemical compound.
Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide) are important commodity chemicals.
Calcium oxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. This is accomplished by heating the material to above 825 °C (1,517 °F), a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2); leaving quicklime. The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it is completely converted back to calcium carbonate.
Annual worldwide production of quicklime is around 283 million metric tons. China is by far the world's largest producer, with a total of around 170 million metric tons per year. The United States is the next largest with around 20 million metric tons per year.
- Heat: Quicklime produces heat energy by the formation of the hydrate, calcium hydroxide, by the following equation:
- CaO (s) + H2O (l) Ca(OH)2 (aq) (ΔHr = −63.7 kJ/mol of CaO)
- As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction. One litre of water combines with approximately 3.1 kilograms (6.8 lb) of quicklime to give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient portable source of heat, as for on-the-spot food warming in a self-heating can.
- Light: When quicklime is heated to 2,400 °C (4,350 °F), it emits an intense glow. This form of illumination is known as a limelight, and was used broadly in theatrical productions prior to the invention of electric lighting.
- Cement: Calcium oxide is a key ingredient for the process of making cement.
- Petroleum industry: Water detection pastes contain a mix of calcium oxide and phenolphthalein. Should this paste come into contact with water in a fuel storage tank, the CaO reacts with the water to form calcium hydroxide. Calcium hydroxide has a high enough pH to turn the phenolphthalein a vivid purplish-pink color, thus indicating the presence of water.
- Paper: Calcium oxide is used to regenerate sodium hydroxide from sodium carbonate.
- Plaster: There is archeological evidence that Pre-Pottery Neolithic B humans used limestone-based plaster for flooring and other uses. Such Lime-ash floor remained in use until the late nineteenth century.
Use as a weapon 
Historian and philosopher David Hume, in his History of England, recounts that early in the reign of Henry III, the English Navy destroyed an invading French fleet by blinding the enemy fleet with quicklime:
D’Albiney employed a stratagem against them, which is said to have contributed to the victory: Having gained the wind of the French, he came down upon them with violence; and throwing in their faces a great quantity of quicklime, which he purposely carried on board, he so blinded them, that they were disabled from defending themselves.
Health issues 
Because of vigorous reaction of quicklime with water, quicklime causes severe irritation when inhaled or placed in contact with moist skin or eyes. Inhalation may cause coughing, sneezing, labored breathing. It may then evolve into burns with perforation of the nasal septum, abdominal pain, nausea and vomiting. Although quicklime is not considered a fire hazard, its reaction with water can release enough heat to ignite combustible materials.
- Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 4.55. ISBN 1439855110.
- Committee on Water Treatment Chemicals, Food and Nutrition Board, Assembly of Life Sciences, National Research Council (1982). Water Chemicals Codex. p. 20. ISBN 0-309-07368-5.
- Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 0-618-94690-X.
- Merck Index of chemicals and Drugs , 9th edition monograph 1650
- Miller, M. Michael (2007). "Lime". Minerals Yearbook. U.S. Geological Survey. p. 43.13.
- Collie, Robert L. "Solar heating system" U.S. Patent 3,955,554 issued May 11, 1976
- Gray, Theodore (September 2007). "Limelight in the Limelight". Popular Science: 84.
- Neolithic man: The first lumberjack?. Phys.org (August 9, 2012). Retrieved on 2013-01-22.
- Karkanas, Panagiotis; Stratouli, Georgia (2011). "Neolithic Lime Plastered Floors in Drakaina Cave, Kephalonia Island, Western Greece: Evidence of the Significance of the Site". The Annual of the British School at Athens 103: 27. doi:10.1017/S006824540000006X.
- Connelly, Ashley Nicole (May 2012) Analysis and Interpretation of Neolithic Near Eastern Mortuary Rituals from a Community-Based Perspective. Baylor University Thesis, Texas
- David Hume (1756). History of England I.
- Croddy, Eric (2002). Chemical and biological warfare: a comprehensive survey for the concerned citizen. Springer. p. 128. ISBN 0-387-95076-1.
- CaO MSDS. hazard.com
|Wikimedia Commons has media related to: Calcium oxide|
- Lime Statistics & Information from the United States Geological Survey
- Factors Affecting the Quality of Quicklime
- American Scientist (discussion of 14C dating of mortar)
- Chemical of the Week – Lime
- Lime production process presentation
- Material Safety Data Sheet