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Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.  






Two or more substances react to form a single product in a Combination Reaction .

A single reactant breaks down into more than one product in a Decomposition Reaction.

Usually, heat or energy is produced in such reactions.

Usually, heat or energy is used in such reactions.

General equation:

A + B  →  C

General equation:

A  →  B + C


CaO(s) + H 2 O(l) → Ca(OH) 2 (aq)


CaCO 3 (s)  →  CaO(s) + CO 2 (g)


In the above two reactions, since the mechanism is opposite , they are called opposite reactions. 

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo