Chemical reactions in which large molecules are built from small molecules are classified as reactions. In contrast, reactions involve breaking large molecules down into smaller ones.

Exothermic and Endothermic Reaction

Explanation:

Chemical reactions in which large molecules are built from small molecules are classified as exothermic reactions. During these reactions, a huge amount of energy is released. When bonds are formed to attain its stability there is the loss of energy as heat energy.  In contrast, Endothermic reactions involve breaking large molecules down into smaller ones. During this reaction, a large amount of energy is involved. When bonds break to attain its stability there is gain of energy.

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