What happens chemically when quicklime (calcium oxide, CaO) is added to water?

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A It undergoes a decomposition reaction and absorbs heat.
B It undergoes a displacement reaction and releases heat.
C It undergoes a combination reaction and releases heat.
D It undergoes a double displacement reaction and absorbs heat.

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Answer: C. It undergoes a combination reaction and releases heat.

Answer: C) It undergoes a combination reaction and releases heat.
Explanation: Calcium oxide reacts vigorously with water to form a single product, calcium hydroxide (slaked lime):
CaO + H2O → Ca(OH)2 + heat
Two reactants combine to form one product, so it is a combination reaction, and a large amount of heat is released, so it is exothermic.

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What happens chemically when quicklime (calcium oxide, CaO) is added to water?

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