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Slowly add water in a small amount of calcium oxide or quick lime containing in a conical flask. Touch the beaker.
Do you feel any change in temperature ?
combination reaction

Objective – Combination reaction with heat change.

Inference – Calcium oxide (CaO) reacts vigorously with water and form a single product, calcium hydroxide (slaked lime).

CaO(s) + H2O (l)   →   Ca(OH)2 (s)  + Heat

This reaction is an example of combination reaction which liberates a large amount of heat (exothermic reaction). So, when the beaker is touched from outside, it feels hot.
Conclusion – In combination reactions, two or more reactants combine to form a single product.