Question
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
✓
Answer
In decomposition reaction, a single molecule of reactant by absorbing heat is broken down into two or more products (atoms), while in combination reaction, opposite phenomenon to decomposition reaction is observed. In combination reaction, two or more substances (elements or compounds) combine to form a single product with heat change.
Decomposition reactions:
$\begin{array}{l} AB +\text { Energy } \longrightarrow A + B \\ 2 AgCl ( s ) \xrightarrow{\text { Sunlight }} 2 Ag ( s )+ Cl _2(g)\end{array}$
Combination reactions:
$\begin{array}{l} A + B \longrightarrow AB +\text { Energy } \\ C ( s )+ O _2(g) \longrightarrow CO _2(g)+\text { Energy }\end{array}$
Decomposition reactions:
$\begin{array}{l} AB +\text { Energy } \longrightarrow A + B \\ 2 AgCl ( s ) \xrightarrow{\text { Sunlight }} 2 Ag ( s )+ Cl _2(g)\end{array}$
Combination reactions:
$\begin{array}{l} A + B \longrightarrow AB +\text { Energy } \\ C ( s )+ O _2(g) \longrightarrow CO _2(g)+\text { Energy }\end{array}$
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