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

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

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Decomposition reactions are called the opposite of combination reactions because of the following:

  • In decomposition reactions, larger molecules break to give simple molecules while in combination reactions, two or more smaller.
  • elements compounds combine to form new compounds.
  • Decomposition reactions are endothermic while most of the combination reactions are exothermic.

For example:

Combination reaction

2H2(g) + O2(g) + Heat ➝ 2H2O(l)

H2(g) + Cl2(g) + Sunlight ➝ 2HCl(g)

Decomposition reaction

CaCO3(s) ➝ CaO(s) + CO2(g)

2Pb(NO3)2(s) ➝ 2PbO(s) + 4NO2(g) + O2(g)

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