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|OTP appearance||white solid|
|Enthalpy of Formation(kJ/mol)||-685|
- Feedstock for calcium hydroxide, lye, and all other hydroxides
- Heat without fire:
- Std Enthalpy of Formation:
- CaO(s) + H2O(l) → Ca(OH)2(aq)ΔH=-63.7
- -635 - 285.83 = -987 - 67
- Does not occur naturally
- Corrosive to skin
- Calcium oxide dust irritates the eyes and lungs
- Mixed with water produces substantial heat as well as calcium hydroxide which is caustic.
From calcium carbonate
- Calcium oxide is produced by heating calcium carbonate above 550°C, often in a lime kiln.
- CaCO3 → CaO + CO2
- Place 100 units by mass of calcium carbonate in a lidded ceramic container
- Place the container in the lime kiln
- Heat to 900°C (orange heat) for 30 minutes
- Remove from fire and measure mass.
N.B. You can use the weight loss to estimate total time to conversion: 100 → 90 is 10 units (out of 44) of mass removed. Estimate 2 hrs to convert all.
- until mass is 56-57 units.
- NB: The above presumes pure calcium carbonate as feedstock. Impurities may increase or decrease the target weight.
- The material is now mostly calcium oxide.
Calcium oxide decomposes when exposed to air along two routes:
- Absorb carbon dioxide from the air to become calcium carbonate
- CaO + CO2 → CaCO3
- Absorb water from the air to become calcium hydroxide
- CaO + H2O → Ca(OH)2
Thus, storage is a problem. For these reasons, calcium oxide is most often used as quickly as it is produced.