Why are decomposition reactions the opposite of combination reactions?

 

• A combination reaction (also called a synthesis reaction) is when two or more substances combine to form a single product.

• A decomposition reaction is when a single compound breaks down into two or more simpler substances.

• Example 1: Combination Reaction

  Reaction:

  $${\text{<br>}}_{}$$2H2​(g)+O2​(g)→2H2​O(l)

  Explanation: Hydrogen and oxygen gases combine to form water.

• Example 2: Decomposition Reaction

  Reaction:

  $${\text{<br>}}_{}$$2H2​O(l)→2H2​(g)+O2​(g)

  Explanation: Water decomposes into hydrogen and oxygen gases — the reverse of the combination reaction above.